ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



457 



cheaper kind. It contains chapters descriptive of the Simple and Com- 

 pound Microscopes and how to use the [Microscope. It tlien deals with 

 some accessories and how to manipulate them, and afterwards describes 

 some common objects. The last two chapters are devoted to the pre- 

 paration and mounting of permanent objects and simple photomicro- 

 graphy. The twenty photomicrographs, which are excellent, were taken 

 by the author, and were obtained by the method described in the con- 

 cluding chapter. 



Beck's Holophane Lumeter.* — The holophane lumeter is a portable 

 instrument (fig. 86) which takes in at a glance the brightness, in 

 candle feet, of any surface. It is a small box, on looking into which is 

 seen an illuminated disk with an aperture in the centre. The object 

 to be examined will be seen through the aperture. It will appear more 

 or less brilliant than tlie surrounding white disk. By moving a handle 

 the brilliance of the illuminating disk can be reduced until it is the 

 same as the object being examined, and the brightness of the object is 



Fig. 86. 



immediately read on a scale of candle feet, the range being from 1/100 

 candle foot to 2000 candle feet. The usual type of photometer deter- 

 mines the brightness of a lamp or other source of illumination, but 

 cannot be used to ascertain the l^rightness of an object or surface. The 

 complete outfit consists of the lumeter, an accumulator, a white screen, 

 and standard candle complete in sling case. 



The lumeter (fig. 87) is a hollow laox measuring G\^ in. by 5 in. and 

 2| in., within which is a circular chamber A, lined with a matt white 

 surface, which contains a small incandescent lamp B ; the box itself is 

 black throughout, except for a matt white screen C, which has a trans- 

 parent aperture D. By means of an eye-piece E, the matt-surface white 

 screen C can be observed, a hole F at the other end of the box allowing 

 an uninterrupted view of objects to be seen through the aperture D. 

 The cyhndrical wall of the inner chamber A has an aperture G- filled 

 with a translucent glass through which light from the electric light B 

 illuminates the white screen C ; its l)rilliance can be increased or 

 reduced by moving the lever H, which revolves a tubular cover which 



Aug. 21st, 1912 2 i 



