Iggul deRav Nahshon; volvelle; putto, rampant lions, vase, Sa'adia Gaon's Haruza; decorated calendar:
Five rotating calendar discs in Zvi Hirsch’s Evronot (MS I:17v-19v) and four in Pinhas' (MS II:64-64v, 67-67v) are designed as alternative systems for determinning the moladot (lunations) and the tekufah (seasons).
The discs (iggulim=circles) also called volvelles, are composed of three or more superimposed rotating paper discs, fixed to the page by a thread. Some of the paper discs, as well as the volvelle on MS II:67 are missing.
the volvelle encloses Rav Nahshon's Circle, which includes the fixed type of years (kevi'ut ha-shanah), the turning of the seasons (tekufot) and the holidays. The circle is supported by two rampant lions, surmounted by a crown with laurel branches flanked by segments of sky, below which are two winged putti. Each is holding in one hand a ball attached by a string to the crown, and in the other a scroll inscribed אורח חיים (Orah Hayim). Two large vases resting on flat bases flank the putti.
The volvelle is surrounded by explanations in red ink. Above the circle:
העגול החיצון מרמז לך באיזה יום שנפל [שנופלת] התקופה עפ"י מחזור גדול; והרבוע הפנימי מרמז לך כמה בחודש נופלת התקופה ע"פ מ"ק (על פי מחזור קטן)
(The external wheel indicates the day of change of the season during the 28-year cycle (Mahzor Gadol); the interior square indicates the day of the month when the season occurs during the 19-year cycle (Mahzor Katan)).
Similar explanations are written in Pinhas' volvelles (MS II:64-64v – fig. 2). In both volvelles the outer disc is inscribed with abbreviated signs for the seasons: תמוז מים דם (Tammuz, water, blood); טבת דם ים (Tevet, blood, sea); ניסן תז (Nisan, tz); תשרי גט (Tishrei, gt), and the She’ilah (שאלת מטר).
In MS I some of these signs, as well as the lions' forelegs, are hidden beneath the rotating disc. For the linking of the tekufah to water, which at the time between one tekufah and the next would turn into harmful blood, see Carlebach (2011:165-169).
Below the disc there is an inscription in red ink which alludes to the "danger of the tekufah" (i.e. the danger at the seasonal change), reading:
טעם למה נותנין ברזל בכלים שיש בהן מים בעת התקופה. מצאתי משום דכתיב עצים ואבנים בדם של יאור [שמות ז, יט] אבל בכלי נחושת וברזל לא היה בהם דם. לכן עוד היום נותנין לתוכן [לתוך הכלים] ברזל כדי להצילם מן התקופה
(The reason why put an iron [implement] into the vessels with water during the change of the tekufah?
I have found [in the Bible] that [vessels of] wood and stones [contained] the blood of theNile[Ex. 7:19], but in vessels of copper and iron there was no blood. So even today some put iron in them [in the vessels] to be saved from [the danger of] seasonal change).
This inscription relates to the custom of not drinking water at the critical time of the seasonal change. This custom appears in halakhic codes, books of customs and Sifrei Evronot, where it was the only religious ritual specifically promoted by calendrical literature in Ashkenazi sources. Although the origin of the custom is obscure, in Pinhas' Evronot, for example (MS II:65v), the explanation for the danger of the unprotected water in the tekufah is that "when the season is changing, one part of the world remains unguarded, and the harmful forces have permission to cause damage, and [exposed] water can be contaminated; therefore people refrain from drinking water at that time".
The halakhic sources mention a number of situations which leave a person vunerable to the danger in the time of the tekufah. One of them is when the drinking water is left uncovered during the seasonal change (Ta-Shma, 2010, ch. 19; Carlebach 2011:160-177; Shalev-Eyni 2014:20-21). According to the 16th-century compilation of halakhic code of Rabbi Joseph Karo (1488-1575), Shulhan Arukh (Yoreh-De'ah 115, par. 5; Orah Hayim 206, par. 6 and 455, par. 1), it is customary to place iron [a metal object] in the drink and foods (sic) at the time of the tekufah. Indeed, Zvi Hirsch left a reference for his halakhic citation by writing "Orah Hayim" on the scrolls of the putti (fig. 1).
Rabbi Joseph Karo modelled the framework of Shulhan Arukh after the Arba'ah Turim of Rabbi Jacob ben Asher (1270-c.1340); and the perpetual calendar, Hilchot Rosh Hodesh in Tur Orah Hayim, is based on Iggul deRav Nahshon. Thus, the inscription "Orah Hayim" on the putti's scrolls may refer to Karo's work, which apparently was within reach to Zvi Hircsh (Nigal 1993:12, 20).