Fig. 48. 
On a Simple Form of Ileliostat. By Thomas Comber. 433 
should be introduced in any part of the system. I cannot, therefore, 
advise the use of a bull’s-eye between the source of light and the sub- 
stage condenser. The angle of the cone of illumination which gives 
the best results, varies, I believe, not only with the object, but also with 
