ARRANGEMENT OF APPARATUS, ETC. Ill 



the edges of the carbon filament being turned to- 

 wards the microscope. 



Connection is now made with the source from 

 which the electricity is supplied. We shall here 

 only mention that electro motors are preferable to a 

 battery, but unfortunately the great expenditure 

 necessary for their maintenance, as well as first pur- 

 chase, puts their application to photographic pur- 

 poses beyond the reach of ordinary individuals. In 

 a late number of the Pliotographic News an electric 

 generator worked by hand is proposed, which may 

 prove practicable if sufficiently low in price. 



If battery power is used, thirty cells of Groves' 

 battery will be found sufficient for a full sized Swan's 

 lamp We have had no experience of the smaller 

 forms recently made, but from a consideration of the 

 character of the light required, we have no hesitation 

 in recommending them. 



One or two cautions are necessary with regard to 

 the batteries, and lamp. Bichromate cells are useless 

 for many reasons but principally for not being suffi- 

 ciently constant. Some means of regulatiug the 

 current is useful, as the sudden passage of a strong 

 current is liable to cause the lamp to burst. The 

 ordinary method of attaching the lamp by a spring 

 is most objectionable, as the slightest movement on 

 the same floor or adjoining apartment, will cause 

 sufficient tremor to utterly ruin the resulting nega- 

 tive. 



The whole stand is now raised to the perpendicular; 

 the microscope stage accurately levelled, and sup- 

 ported in that position by lengthening the camera legs. 



