204 



THE AMEEICAN MONTHLY 



[November, 



Too much attention cannot be 

 given to the course of rays which im- 

 pinge upon the mirror of the micro- 

 scope. It w^ill be understood thatw^e 

 now allude to woi'k of a delicate na- 

 ture, in which the capabilities of the 

 microscope are severely tested. All 

 illuminating apparatus is constructed 

 to work most perfectly with parallel 

 rays of light. Consequently, when 

 using any ' sub- 

 stage apparatus — 

 condenser, para- 

 boloid, or other 

 device — it is de- 

 sirable that a 

 beam of parallel 

 rays be directed 

 upon the mirror. 

 The rays from a 

 lamp can be made 



approxi- 

 mately par- 

 allel by pro- 

 p e r 1 y a r - 

 ranging a 

 bull's-eye 

 lens in front 



Fig. 26. — Beck's New Complete Lamp. 



rious anglesby means of a milled head 

 acting against the started pin K. By 

 temporarily removing the upper part 

 of the chimney F \k\& condenser can 

 be swung over to the other side, and 

 the beam can then be directed down- 

 ward, below the horizontal, as would 

 be required to illuminate opaque ob- 

 jects. By sliding the condenser 

 along its support, the light may be 

 rendered parallel or convergent, 

 as may be desired. 



The chimney and the reservoir 

 containing the oil are independent 

 of each other, and the latter, with 

 the burner, can be revolved, thus 

 presenting the edge or the flat side 

 of the flame at will. 



The lamp slides up and down 

 on the square upright B ; when 

 in its lowest position the flame is 

 only three inches above the table 

 on which it stands. 



One fault in this lamp, which 

 i m m edi- 

 "^ ately sug- 



gests it- 

 self, for- 

 t u n a tely 

 one easi- 

 ly reme- 

 died, is 

 the neces- 

 sity of re- 

 moving 

 part of 

 the chim- 

 ney a n d 

 turning 

 the con- 

 denser 

 over to 

 the other 

 side to 

 obtain a 

 beam di- 

 re c t e d 

 d o w n - 



of it. In the lamp now under consider- 

 ation the bull's-eye P slides upon a 

 bar X, in front of the aperture j^in 

 the metal chimney. The bar L 

 swings on pinions at //, which en- 

 ables the bull's-eye to be set at va- 



ward. It is especially inconveni- 

 ent to do this after the lamp has 

 been burning a short time, as the 

 metal chimney becomes very hot. In 

 fact, we may assure every intending 

 purchaser of any of these lamps that 



