1016 



SUMMARY OF CURRENT RESEA.ROHES RELATING TO 



two horse-power, and supplying an arc light of about 1200 candle-power. 

 This is sufficient for a linear amplification of 1000 ; but for oil-immersion 

 or for high-power dry systems an illuminator is required. An achromatic 

 condenser has accordingly been designed by Prof. Abbe, as the ordinary 

 chromatic Abbe condenser cannot be used for the purpose. The bright- 

 ness of the image is increased to an extraordinary extent by the achromatic 

 Abbe condenser, and, so far as 1 can estimate, is nearly equal to that which, 

 without this system of lenses, would only be attained by an arc light of 

 2500 candle-power. Since the condenser is only used with the higher 

 powers, it requires a simple adjustment by which it can be removed. The 

 brightness of the image can, of course, be considerably increased by using 

 a more powerful source of light. 



The construction of the lamp (fig. 240) has been left entirely to the 



Fig. 240. 



mechanician. A is a rectangular plate of cast iron into which the cylin- 

 drical iron rod B is set, and fixed by two iron stays= At the height of the 

 table is a shelf C for the objects not in use. Above the shelf are the two iron 



