590 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Fig. 66. 
am ^6 
4 in., and the ten sets are arranged on an arc 
of 75 cm. radius. The formation of the inverted 
image which is seen when the concave side of 
the Lampyris-e , ye is turned towards the object 
is explained by fig. 67. The crystalline cone 
acts like an astronomical telescope adjusted for 
infinite distance. The deviation which a ray 
undergoes is shown in fig. 68. 
ab = ab x tan a = a h 2 tan /3. 
Denoting the focal lengths a7q, ah 2 by </> l5 0 2 
tan a 
tan p 
— = const. ; 
0i 
or, sin a = 0 2 sin /3 since a, /3 are small. 
The rays incident on the eye will be de- 
flected in each crystalline cone according to the 
above law, and by means of it the calculation 
of the image, optical constants, &c., follows in 
a way strictly analogous to that of an ordinary 
lens. 
Let be (fig. 69) be the curvature of the 
eye, ap a radius from the centre of cur- 
vature a, p c a ray from the point p, which is 
deflected to d. 
Then by the above law, 
sin pea ap 
0 2 _ sin ped _ sinpea _ sin cap cp 
0 X sin qc a sin qca sin qc a ~ a q 
sin c ap c q 
<h ' cp _ap 
<f) 1 c q a q‘ 
For rays near b 
cp = bp = _J\_ # 
cq~ bq -f 2 
• ^2 fl = a P = fl + r 
01 ’-/ 2 a( L V + f 2 
which leads to the equations 
01 , 02 _ 01 + 0 2 
fi A ~ r 
01 _ 02 _ 01 + 0 * 
92 9l ~ 
where g v g 2 denote ap, a q. 
— r 
