298 The Magnesium and Electric Light ["ounuLVjEwa' 



The Magnesium lamp (a) stands on a shelf fastened against the 

 wall. The condenser (6) concentrates the light on the lower lens 

 of the achromatic condenser of the microscope (c), which stands on 

 a table (e), supported on three levelling screws. The image received 

 on the plate holder [g), which is supported on a table (/), is 

 photographed precisely as in the case of the Electric light as above 

 described. The same focussing apparatus {d) is employed, and the 

 ammonio-sulphate cell should invariably be inserted, but the ground 

 glass is never necessary. I find that it requires exposures of about 

 three minutes to produce negatives of tissue-preparations with five 

 hundred diameters. Other powers require proportionate exposures. 



The Magnesium lamp used by me for this purpose was the two- 

 ribbon lamp of the American Magnesium Company (No. 2, Liberty 

 Square, Boston, Mass.), sold by that company for magic lantern 

 purposes, price 850. The ribbon weighs about 52 centigrammes 

 per metre, and is sold at S2.50 per ounce. Two ounces will, with 

 care, answer for three or four hours' constant work, and ought to 

 produce from twelve to thirty negatives, in accordance with the 

 difficulties of the subjects to be represented. The fumes of magnesia 

 resulting from the combustion are carried into a chimney five feet 

 long, made of a spiral wire covered with muslin, which terminates in 

 a muslin bag, in which the oxide condenses, while the draught goes on 

 through the interstices of the muslin. The chimney and bag are 

 fornished by the company for ^2.50. 



In commenting on the above processes it may be remarked that 

 for the anatomist and physiological investigator, the Magnesium 

 lamp affbrds a satisfactory and sufficient source of light for the pho- 

 tography of normal and pathological tissue-preparations. The same 

 end can be equally well or even better attained with the Electric 

 lamp, with which also the most difficult test-objects can be satisfac- 

 torily reproduced. Where economy of apparatus is the object, the 

 Magnesium lamp will be preferred by ordinary workers ; but where 

 much work is to be done, the high price of the Magnesium ribbon 

 more than counterbalances the cheapness of the apparatus, and the 

 Electric hght becomes the most economicil. For the information 

 of any practical photographers who may be employed for work of 

 this character, I may add the following remarks on the chemical 

 process employed in the production of the negative from which the 

 appended prints were made. An ammonium and potassium portrait 

 collodion, rich in alcohol, was employed, developed with the ordinary 

 solution of iron, and fixed with cyanide of potassium. Where it 

 was necessary to intensify, the hydro-sulphuret of ammonium was 

 resorted to. 



In illustration of the character of these sources of illumination 

 as compared with each other and with sunlight, I herewith append 

 three prints from negatives, taken with a Wales' inch and a half, 



