"ouruil/junfi'S] «« ai^pUed to Plwto-micrographij. 293 



of microscopic objects can be conveniently produced with these 

 artificial lights. 



1. The Electric light is by far the best of all artificial lights for 

 the production of Photo-micrographs, and when used, as I am- now 

 about to describe, it is both convenient and economical. I use a 

 Grove's battery of fifty elements. The battery is jjlaced just outside 

 of the operating room in a closet, from which the fumes escape 

 through an earthen pipe into the main chimney of the building. 

 This battery was furnished by Mr. William Ladd, Nos. 11 and 12, 

 Beck Street, Eegent Street, London, W, The rubber cups are 4f 

 inches high, 3|- wide, and 2 tliick. The platinums are 5|- inches by 

 2i, and weigh about 60 grains each. The zincs are bent on them- 

 selves so as to present a part of theii' surface on each side of the 

 platinums, and weigh, when new, about a pound apiece. Mr. Ladd 

 furnishes these batteries in trays of ten elements, at five pounds 

 sterling per tray, and I find that a battery of five trays is sufficient 

 for most purposes. Seven pounds and a half of strong commercial 

 nitric acid, and three of sulphuric, diluted with ten times the quan- 

 tity of water, is sufiicient to charge this battery, which will then 

 produce the light continuously for from three to four hours. The 

 cost of running the battery for this time, including in the estimate 

 the amount of zinc consumed, and the cost of amalgamating every 

 third or fourth time of using, is very moderate. I make it a prac- 

 tice to have the battery washed out, the acids thrown away, and the 

 porous cups put to soak immediately after I have done the day's 

 work, and all this is so simple that I have had no difiiculty in in- 

 structing an orderly to do it, so that the management of the battery 

 does not occupy any part of my time. 



The Duboscq's lamp, the microscope, and the plate holder are 

 arranged in a dark room, which enables me to dispense with the 

 use of a camera. The general arrangement of the apparatus is 

 shown in the cut (see next page). 



The Electric lamp of Duboscq (a) is placed on a stool against 

 the wall at one end of the room, and its light concentrated by a 

 pair of condensing lenses (b) on the lower lens of the achromatic 

 condenser of the microscope. The microscope (c) (a large PoweU 

 and Lealand's stand) is placed on a small table (e) which is so 

 arranged that it can be lowered or elevated at pleasure, and can be 

 levelled by means of three levelling screws at its base. The j^late 

 holder {g), also arranged so that it can be raised or lowered at plea- 

 sure, is supported by a small table (/) which stands on three level- 

 ling screws. The floor of the apartment is quite level. The lenses 

 employed for the microscopes are those of Mr. Wilham Wales, of 

 Fort Lee, New Jersey, specially constructed for bringing the actinic 

 rays to a focus. For powers above the ^th, however, I have found 

 that the achromatic objectives of Messrs. Powell and Lealand, of 



