The “academic hour” was 45 minutes long, giving professors time to prepare for the next class and for students to get there.
In his first few years, Kant lectured in the mornings and occasionally in the afternoons, but by the mid-1760s nearly all his lectures were in the morning, although apparently never before 8 AM. Upon his promotion to professor of logic and metaphysics in 1770, he was required to hold public lectures (logic in the summer, metaphysics in the winter) from 7-8 on the main lecture days (Monday, Tuesday, Thursday, Friday). From a 1797 note of Kant’s we learn that “in 1770 when I became the logic-metaphysics professor, whereby my lectures were set at 7 AM, I had to hire a servant to wake me.”
By law each professor here must hold a weekly class [collegium] publice or for free for four hours. It is even prescribed of the philosophers that for the sciences for which he is employed, e.g., for Kant Logic and Metaphysics, for myself Ethics and Natural Law, each must read for free weekly during four expressly determined hours (Kant mornings at 7, I at 8 o’clock), and that the sciences must be completed at the end of each semester.
This regulation of the hours that Kraus mentions must refer to an internal rule of the University, since it is not part of the 1735 edict handed down from Berlin.
Successfully completing the material of a course of lectures in one semester was apparently a problem at the university. Hippel [bio] wrote that “in my day [namely, beginning with WS 1756/57], no course was completed in one semester. Many courses, and even the most necessary (or “Brot Collegia”) would last two years” [qtd. in Arnoldt 1908-9, v.182]. This problem was addressed in an edict of 14 April 1768, signed by Braxein and v. Korff: “Of the professors in the philosophy faculty, and not least of which certain lecturers (Magistris legentibus [glossary]), we hope they proceed diligently and actually finish, in a respectable way, what they say they will do” [qtd. in Arnoldt 1908-9, v.217]. Arnoldt believes that this comment could not have applied to Kant, but we do find in at least one semester — SS 1766 — an indication that Kant was finishing up material from the previous semester for both his metaphysics and his moral philosophy lectures (it appears that he held the additional lectures on Wednesday and Saturday; apart from these, he was beginning the following courses that semester: logic, metaphysics, moral philosophy, and physical geography).
 We hear from Reichardt [repr. in Malter 1990, 80-1] that Kant took twenty minutes between lectures to prepare, but many of the details given by Reichardt appear to be unreliable.
 Borowski, as reported in Reicke [1860, 32; reprinted in Malter 1990, 43].
 Quoted in Brandt/Stark [1997, cii]. Lighting would also have been an issue in the winter months. There were only three small windows in Kant’s lecture hall (at Princessinstrasse), which would have been of little help near the winter solstice, when the sun rose at 9 AM and set a little before 4:30 PM.
 Krause [1920, 69].
In order that the professors have some rest from their work, and so afterwards will proceed with greater energy, and similarly that the students of the courses are better able to study the material and finish anything given them, it is written in the Constit. acad. Tid. de Feriis that the professors at this university should be free from lecturing on Wednesdays and Saturdays, and are permitted to lecture for only four hours per week [per class], which is confirmed in ch. 6 of the Statut. acad. [Arnoldt 1746, i.191]
This according to Daniel Arnoldt’s 1746 history of the Albertina. Most lecture courses met for a total of four hours per week, generally meeting on the main lecture days (Monday, Tuesday, Thursday, and Friday), and took place sometime between 7-12 and 1-4. Kant also regularly taught courses that met on Wednesdays and Saturdays for two-hours each day.
The academic year was divided by the Feast of St. Michael (September 29) and Easter, with the summer semester occurring from Easter to St. Michael and the winter semester occurring from St. Michael to Easter. St. Michael was a fixed date, but Easter fluctuates from year to year (since it falls on the first Sunday after the first full moon after the spring equinox, which is March 21). The date for Easter can thus be anywhere from March 22 to April 25, thus creating a possible difference in length between any two semesters by more than a month. With each new semester also came the election of the new rector for the university, which takes place “on the Sunday after Easter for the summer semester, and on the next Sunday after the Feast of St. Michael for the winter semester.” The election of the rector is an important academic date, but it was not the beginning of classes, since the distribution of the Lecture Catalog (Vorlesungsverzeichnis) was to occur “eight days after the election of the rector at the beginning of each semester” [Arnoldt 1746, i.199].
The Berlin Ministry issued a reprimand to the university on August 30, 1784, “against certain obstructions and misuses which have recently disturbed the dutiful operation of the business of teaching and the good order of the university in general” [Arnoldt 1908-9, v.279; the records are at GStA XX.HA. EM 139b,28]. The university defended itself the following month (September 24, 1784) with a document, the first part of which contains the following passage:
While public lectures are viewed as mere side-affairs or opus supererogationis at other universities, here they are viewed by every upright teacher who knows our students and takes to heart the well-being of our land as the foundation of academic instruction. Thus, for some of these courses, their content and hours are held with a fidelity beyond the call of duty, and so are known to the students even without the Catalog of Lectures. These lectures are therefore begun the very day after the distribution of the Catalog by many teachers, for instance the professor of logic [i.e., Kant], and by most of the other teachers by the following Thursday or Monday; and since the greatest number of students attend these public lectures, they find here the best opportunity to have already chosen which of the private lectures they want to attend, according to their needs and long before the distribution of the Catalog, and so are able to coordinate their courses in the event of a time-conflict; and so even a good number of the private lectures begin in the same week or the week immediately following.
The diary of Christian Friedrich Puttlich [bio], who entered the university at Königsberg on 23 March 1782 and took several courses with Kant, reveals that Kant was in fact operating in accordance with this report. In 1782, Easter fell on March 31, so the new rector elected on Sunday, April 7. By statute the Lecture Catalog need not be issued until eight days following this election: in this case, April 15 (Monday). Puttlich, who attended Kant’s logic lectures that semester, notes in his diary that the first class period was on Monday, April 15. Kant’s lectures on Physical Geography, given on Wednesdays and Saturdays from 8-10 each day, began that Wednesday (April 17). The following winter semester began a few days later than normal since St. Michael’s fell on a Sunday, pushing the election of the rector off a full seven days to October 6, with the Lecture Catalog being distributed on October 14; and again we find Kant beginning his course on Metaphysics that very Monday, October 14, and his lectures on Anthropology that Wednesday, October 16 (as with Physical Geography, he would teach Anthropology on Wednesdays and Saturdays; these four courses were his academic mainstays, alternating between them with Logic and Physical Geography in the summers, and Metaphysics and Anthropology in the winters.
 From the Statutes of the University at Königsberg, reported in Arnoldt [1746, ii.88]. If St. Michael fell on a Sunday, then the new rector would assume office the following Sunday.
 Kant’s course on physical geography for SS 1757 was entered into the faculty minutes on April 13 (the Wednesday following Easter); for SS 1758, it was entered on April 1 (the Saturday following Easter); for SS 1759, April 28 (the Saturday after the election of the rector); for SS 1761, April 6 (the 2nd Monday after the election of the rector, and what should be the first day of classes); for WS 1761/62, October 11 (the Sunday after the election of the rector); for WS 1763/64, October 10 (the 2nd Monday after the election of the rector); for WS 1765/66, October 13 (the Sunday after the election of the rector).
 GStA XX. HA EM 139b, 28.
It is an ugly affair with these far too long vacations, which are longer in Halle and Leipzig than in any other German university. Indeed some Halle professors shorten the vacation by continuing to lecture even if all the students are gone, but many take seven weeks of vacation in the spring, six in the fall, one at Pentecost and two at Christmas, and that makes for sixteen weeks of vacation in the year, and dedicates more than a fourth of the year to idleness; for the students hardly study at all during vacation, as I know from experience.
Kant had on average sixteen weeks free each year from teaching responsibilities. This practice of long periods of time free of lectures is an old one. In the universities of the middle ages, four months were also given over to idleness.
A royal decree from Berlin of 18 October 1732 (and repeated again in the decree of 1735), argued that the “harvest vacation” should be eliminated and the others restricted — namely, Christmas and Easter break were to be restricted to fourteen days, and Pentecost to eight. The decree stipulated that students who left for harvest vacation without permission from the faculty would lose any stipend they were receiving and, if they were not receiving any, their names would be recorded to exclude them from any future stipends. The faculty senate justified itself by noting that it had no control over the student’s behavior in this regard [Arnoldt 1746, i.369-70, Appendix #54; see also Gause 1996, ii.114].
Borowski notes that, for Kant’s part, “the lectures were held with punctuality and conscientious fidelity, allowing only those vacations that were legally allowed” [Borowski 1804, 85]. Rink offers the same assessment: “he remained up to the end a very conscientious teacher, and I can’t recall of a single time, other than the usual vacations, that he did not hold class” [Rink 1805, 46-47; repr. Malter 1990, 157-8].
 From the autobiography of Magister Friedrich Christian Laukhard (1758-1822), who did not attend Königsberg; see Laukhard [1792, ii.222].
 This decree was doing little more than repeating the university statutes of 1554 that stipulated the same length of time for each vacation, but leaving the length of the summer vacation to the discretion of the academic senate [Bornhak 1900, 35]. (The relevant archive material is at the GStA, with the signature: XX. HA M 139b, 28).
We have no records of Kant’s early teaching career, so it cannot be determined with certainty how he proceeded; but a dispute between the lecturers and the professors as to when they could begin the semester suggests that the lecturers were eager to start the semester as soon as possible (likely in part because that was their source of income). (See the discussion of this dispute at Kant’s Lecture Announcements).
Dog Days (dies caniculares) is the time from July 23 until August 23, beginning with the early setting of the dog star, Sirius — whence the name — and ending with the early rising of Arcturus (which is actually much later than the end of our dog days). This is also generally a time for harvesting certain crops, and so the university vacation around this time was variably called the Dog Days vacation or the Harvest vacation. In an August 1727 letter of Georg Friedrich Rogall [bio] we learn that: “It is now dog days, when no lectures are held at the university for six weeks, because the non-local students go home to their families” [Wotschke 1928, 103]. Kant often spent this time in the country.
We saw above that this harvest vacation was to be eliminated in 1732, yet the Berlin government was still complaining about it in an edict of August 30, 1784: “the so-called Harvest Vacation, which lasts four weeks, although neither teacher nor student are in any way occupied with the harvest, shall last no longer than eight days.” The academic senate defended itself:
“We can say with certainty that for many years about one-fourth of the students are foreigners, and the other three-fourths are Prussian born; and these many natives [Einländer] have always, for whatever reason, found it necessary to travel to their families at harvest time.”
Evidence of this vacation is found in contemporary letters, as well as in the lecture notes themselves. In a letter to Marcus Herz dated 20 August 1777 [AA 10:211, #120], Kant mentions a surprise visit by Moses Mendelssohn [bio] to two of his lectures “the day before yesterday,” noting that “he must have found the lecture somewhat chaotic this time, since I had to repeat that which had preceded the vacation, and this also took the greater part of the hour.” August 20th fell on a Wednesday that year, and so the visit occurred on August 18 (Monday). On Mondays of that semester Kant was teaching Logic (7-8 AM) and Natural Law (8-9 AM), so these are apparently the lectures Mendelssohn attended. The fact that he had arrived in Königsberg on July 24 (Thursday), and had only now visited Kant, suggests that the recess was already in progress when he had arrived, and that Kant had already left for the countryside; this suggests that summer vacation lasted at least four weeks that year.
There are other reasons to believe summer vacation lasted four weeks, such as the cited regulation about “the four week-long vacation should not last longer than 8 days.” In a letter from Kiesewetter to Kant (20 April 1790; AA 11: 155-60, #419), he proposes to visit Kant during the dog days vacation and to stay in Königsberg fourteen days (the trip from Berlin to Königsberg and back would have consumed the remaining two weeks). Also, we find the following entry in the logic notes of Graf Dohna-Wundlacken (stemming from SS 1792): “Tuesday, the 17th. NB. Here Kant took a vacation of more than 4 weeks” [AA 24: 771; Kowalewski 1924, 109]. The date on the next page (“Monday the 20th of August”) suggests that the summer vacation must have begun on the 17th of July (1792), which was indeed a Tuesday. In the Bauch logic notes, Friedrich Bauch wrote down “23rd Aug. 94” as the resumption of classes for SS 1794. And Christoph Coelestin Mrongovius apparently used the summer vacation in August 1784 to write out a fair copy of his notes of Kant’s lectures on natural theology that he attended during the previous semester (WS 1783/84).
During Kant’s early years as a lecturer we find Johann Gottfried Herder [bio], who matriculated 10 August 1762, appearing in Kant’s classroom “for the first time” on 21 August 1762. This fell towards the end of the summer semester, and the fact that he did not wait until the beginning of a new semester, and yet waited eleven days to begin, suggests the summer vacation was in progress when he arrived.
 Christian Jacob Kraus [bio], while a student at Königsberg, also mentions this in a 29 July 1778 letter to his brother in Elbing, whom he was planning to visit during the coming weeks:
[...] You are perhaps worried that, since the Dog Days are nearly half over, that I won't be able to stay long with you. My dear brother, the Dog Days are nothing to me. I interact quite comfortably with several professors, as with my friends, but I’ve had nothing to do with their classes for some time now. I’ve had Dog Days ever since Easter, although I've worked more in that time than others do in the entire year [Krause 1881, 90].
[...] Du besorgest vielleicht dass ich wegen der Hundstage die alsdann beynahe schon halb zu Ende seyn werdern, mich nicht bey dir werde verweilen können. Mein bester Bruder, die Hundstage gehen mich nichts an. Ich gehe mit einigen Professoren als mit meinen Freunden recht vertraulich um, aber mit ihren Collegiis habe ich seit langer Zeit nichts zu thun. Seit Ostern habe ich immer Hundstage gehabt, wie wohl ich in der Zeit mehr gearbeitet habe, als andre im ganzen Jahr.
 The senate’s reply was dated September 24. Arnoldt [1908-9, v.279] wrongly believed that the vacation at issue here was just the Michaelmas vacation following the summer semester.
 See Kant’s letter to Herz (Friday, 31 August 1770), writing about Herz having just been in Königsberg to serve as Respondent at Kant’s dissertation defense on August 21 (a Tuesday): “I have not felt well these past days, and now this pile of classes starting up again has not let me find time to recuperate enough to think about the promised letters” [AA 10: 95, #55]. Also a letter from Schultz (21 Aug 1776): “Since the last two vacation weeks have finally permitted me the long desired leisure to think through your criticism in its context; ... ” In Kant’s letter of 5 August 1784, to Linck we read that one of Kant’s students, of whom he attests diligence and skill, is “now in the country in order to use the vacation, and will return from there in 10 or 12 days” [AA 10:395, #234]. Finally, in Graf von Dohna-Wundlacken’s notes from Kant’s lectures on physical geography from summer semester 1792, we find Kant taking a five week vacation from between Wednesday, July 14, and Wednesday, August 22 (Between these dates we find the comment: “NB Hier fing Kant seine Ferien an, welche 5 Wochen währten.”
 See a letter from Hamann to Kraus (dated August 7, 1786): “The main cause of my writing is the concern of your landlord and landlady that you not arrive before the end of the vacation. Your rooms are still open, they are working as hard as they can until 9 in the evening; but they don’t think it’s possible to be done before this date” [Henkel 1975, vi.524].
 The dates “19th July ... 19th August” are on the manuscript, clearly the beginning and end of something, and it was not uncommon for copyists to date their copying activities in this fashion. Kurt Beyer, who had worked with the manuscript but had not considered the possibility discussed here, believed that the manuscript was a copy, and not a set of notes written in the lecture hall; see Beyer [1937, 231].
 This was in Kant’s metaphysics lectures. At the top of Nachlaß-Herder XXVI.5 [AA 28: 1486] we read: “with Kant the first time, the 21 August, on pneumatology,” followed by two pages of metaphysics notes.
Pentecost falls on the 50th day after Easter, and therefore also floats in the calendar between May 10 and June 13. We have little documentary evidence for a vacation over Pentecost [Pfingsten], except for the edict of 18 October 1732 which limited it to eight days. Also, F. J. Buck [bio] wrote of several one- to two-week vacation trips over Pentecost from Königsberg to Pillau [Buck 1775].
The contours of Christmas vacation (Weihnachtsferien) appear in several of the lecture notes. Graf Dohna-Wundlacken left us notes from Kant’s anthropology lectures (Dohna-Wundlacken 1), which he attended in WS 1791/92, and many of the entries are dated, making it clear that Kant cancelled classes for about one month around Christmas. On p. 103 of the manuscript we read “29th hour Wednesday the 30th November”; on p. 105: “30th other [i.e., the second] hour from 9-10”; on p. 120: “32nd hr. f 9-10”; and on p. 124: “33rd hour Wed the 4th January 1792” — thus one additional class was taught between Nov. 30 (Wednesday) and Jan. 4 (Saturday). The Graf’s metaphysics notes from the next winter semester (Dohna-Wundlacken 4) are divided into 73 hours; there were 92 hours (days) available between the first and last class meeting, leaving 19 days (about five weeks) of vacation within the semester, most or all of which would have been the Christmas break.
Such dates can be misleading, however. Friedrich Wilhelm Pohl matriculated at the university on April 28, 1780, and in his notes from Kant’s anthropology, various dates appear to give us an indication of Christmas vacation and its length. In the margin of p. 212 of the manuscript is written “1781 the 2nd Jan.”, which Otto Schlapp supposed was the date for the resumption of classes after the vacation [Schlapp 1901, 12] — although this is much less likely when one discovers that January 2 was a Tuesday, and the class met on Wednesday and Saturday. At the end of the notes is the date: “13th Feb. 1781”, also a Tuesday, and about six weeks before the end of the course (on Saturday, March 31). These particular dates clearly concern something other than the rhythm of the course.