ARRANGEMENT OF APPARATUS, ETC. 95 



sources of light ; not on account of any advantage 

 gained by using the illumination and arrangement 

 described with that particular objective. For in- 

 stance, sun light, lamp light, and electricity, give 

 equally good results with the eighth immersion ; if 

 the adjustments of the microscope are suitable for 

 this objective, and the conditions of their employ- 

 ment identical. 



With regard to illumination, we most decidedly 

 recommend the use of an ordinary parafin lamp, 

 with one broad single wick, one and a quarter inch 

 or more in width, in preference to all other kinds ; it 

 is always obtainable, requires little care, and the ex- 

 pense incurred is very trifling. 



If properly employed a negative can be taken by 

 this light in five minutes, with the one twenty-fifth, 

 having a magnification from 1000 to 5000 diameters, 

 which will bear subsequent enlargement to 50000 

 before the finest details become visible to the naked 

 eye. 



Swan's incandescent lamp has numerous advan- 

 tages, among which may be mentioned the facility 

 of focussing, on account of the whiteness and bril- 

 liancy of the light, and the possibility of placing the 

 apparatus in any position during its employment. 



Care should be taken that the carbon filament 

 occupies the centre of curvature of the glass globe, 

 otherwise aberrations will be produced by the inclin- 

 ation of the surfaces ; this might be avoided by par- 

 tially flattening the globe on two sides, one being 

 behind and another in front of the edge of the carbon 

 filament. 



