e Tithonometer. 221 
Prof. Draper’s Deserip. 
‘that the great increase of 
that the flame is drawn vio- 
plate by the current established 
stand. It will be easily und 
light arises from the cirew 
in the cylinder. 
As much radiant 
diminish its action, an 
S emitted by this flame, in order to 
so to increase the tithonic effect, I adopt 
t. Let A B, fig. 4, be the lamp; the 
e received on a convex lens D, four inches 
in diameter, that which I use being the large 
This, placed at a distance of twen- 
sig ice’ of ffirteen inches, white is Ss cabvelh on the sentient tube 
‘of the tithonometer F'; between the tithonometer and the lens 
there is a screen E. 
Things being thus arranged, and the lamp lighted so as to give 
a flame about three inches and a half long, we may proceed 
with the experiments. It is convenient always to work with the 
flame at a constant height, which may be determined by a mark 
on the glass cylinder. Ata given instant, by a seconds watch, 
the screen Eis removed, and immediately the tithonometer be- 
_ gins to descend. When the first minute is elapsed the position 
on the scale is read off and registered ; at the close of the second 
minute the same is done, and so on with the third, &c. And 
now, if those numbers be compared, casting aside the first, they 
will os found equal to one another, as the following table of ex- 
periments, made at different times and with different instruments, 
shows :— 
Taste I, — Showing that when the radiant source ts constant, the amount 
of movement in the tithonometer is directly proportional to the times 
of exposure. 
a ee eg 
Papert hah 
oTime:» | scm Weeds Bgl * E 
30” 700 7-00 | 10:25 oat 5-25 
60 800 7478 | 11-60 11:75 6:50 
9 7:50 8-00 11-50 ae 6-25 
120 7:75 7-75 11:50 13-00 6-00 
150 75 7:25 Lae ee 6-00 
180 Py {64 or 12:00 6-00 
es, NEEL on eee. 6-00 
Mean 760. | “7-66 11°19 | 12°25 6-00 
