3, No. 4), may be equal to the
declination of the sun on the day of observation. It is precisely to
this end that the names of the months are inscribed upon the slide....
[Illustration: FIG. 1.--TRAVELER'S SUN DIAL.]
The accessories of the instrument are as follows: A ring with a pivot
for suspending the meridian circle, and the position of which, given
by a division in degrees marked upon this circle, must correspond with
the latitude of the place; two stops serving to fix the position of
the equator circle; finally the latitude of various cities. The
instrument was constructed at Paris, by Butterfield, probably in the
last quarter of the eighteenth century.
The second instrument, which is of the same nature as the cubical sun
dial--that is to say, with horary angle--is, unlike the latter, a true
trinket, as interesting as a work of art as it is as an astronomical
instrument. It is a little mandolin of gilded brass, and is shown of
actual size in Fig. 2. The cover, which is held by a hook, may be
placed in a vertical position, in which it is held by a second hook.
It bears in the interior the date 1612. This is the only explicit
historic datum that this little masterpiece reveals to us. Its maker,
who was certainly an artist, and, as we shall see, also a man of
science, had the modesty not to inscribe his name in it.
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