716 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fig. IGO. 



that one would hesitate to mention them, unless frequently confronted 

 with error. 



Fig. 159 shows the correct method of illuminating with diffused 



day- light, no'substage con- 

 FiG. 159. denser being used. P the 



plane of the object. C the 

 concave mirror. The mir- 

 ror is placed at the distance 

 of its principal focus from 

 the object. 



Fig. 160 shows the 

 rough and ready and, I am 

 sorry to say, too often, the 

 usual style. 



Fig. 161 shows the 

 correct method of illumi- 

 nating for dark ground, 

 with substage condenser 

 and stops. E, edge of 

 flame ; B, bull's-eye ; m, 

 plane mirror ; S, substage 

 condenser. 



Fig. 162 is another ^ 

 correct method of doing the 

 same thing by using the 

 concave mirror and no 

 bull's-eye. It is seldom 

 used, as it is very difficult 

 to set up. 



Fig. 163 shows the 

 error of using the concave 

 mirror with the bull's-eye. 

 Many do it, thinking that 

 they get more light. 



Fig. 164 shows the 

 error of not having the edge 

 of the flame E in the prin- 

 cipal focus of the bull's-eye 

 B. This teaches how im- 

 portant it is to have the 

 bull's-eye fixed to the lamp, 

 so that both may be moved 

 together, and not indepen- 

 dently. The author's own 

 bull's-eye is so made that 

 when it is pushed home in 

 its slot, the lamp flame is in 

 its principal focus. 



To set up fig. 161 

 correctly, with a bull's-eye 



