182 THE AMERICAlSr MONTHLY [Oct. 



tive Committee, Professor S. H. Gag-e, of Ithaca ; Dr. A. 

 Clifford Mercer, of Syracuse, and Dr. V. A. Moore, of 

 Ithaca; 



Lime Light. — The surface of the lime is not so evenly 

 incandesced as that of carbon. It g-ives a small homoge- 

 neous point of ligfht and quite intense. But "by reducing- 

 the pressure of the g"as to about one inch and using- a very 

 hard lime and a jet w^ith a medium-sized bore a fairly 

 steady lig-ht is obtained. Still the arc lig-ht is better. 



Electric Arc Lamp. — There has been g-reat diflBculty in 

 using- this lig'ht for photomicrog-raphy because the position 

 of the arc was not constant and the source of lig-ht not 

 uniform. Messrs. Barnard and Carter of the Quekett 

 Club devised a form in which the distance apart of the 

 carbon points is reg-ulated by hand, their position thus con- 

 trolled easily. By reference to cross-wires on a g-lass 

 screen the source of lig'ht can always be kept in the same 

 place. The oblique position in which the carbons are set 

 enables the small point of intense lig-ht from the incan- 

 descent crater of the positive carbon is used as a source 

 of unvarying- and steady illumination of small area and of 

 very g-reat intensity. 



Dry Mounts. — The Postal Microscopical Club people 

 have been discussing- dry mounts and appear to disap- 

 prove of them as liable to deterioration. The g-reat differ- 

 ence of refractive index between the objects and the air 

 which makes them nearly opaque from total internal re- 

 flection of the lig'ht results in fogg-y imag-es and often 

 totally obscures the structure. A medium of hig-her 

 refractive index should be used for hyaline forms like 

 diatoms, even hig-her than balsam for very thin forms. 

 During- mounting- the org^anic matter is burned out by 

 heating- the cover-g-lass. During- this process, some of the 

 forms may be melted into the cover-g^lass. They may be 

 observed profitably if the g-lass be made with the same 

 refractive index as that of the front lense of the objective. 

 A common accident to the mount is the running- in of the 

 cements but this accident sometimes chang-es the dry 



