ARRANGEMENT OF APPARATUS. 107 



beyond the reach, of private individuals, in fact, 

 until electricity is supplied by accumulators or from 

 a central station, parafiu will be found far superior. 



The actinic power of the electric light is inferior 

 to the intensity of its illumination, allowance must 

 be made for this when judging of the time necessary 

 for correct exposure. 



The lamp should be covered and mounted in the 

 same way as the parafin lamp before described ; or 

 one may be substituted for the other, if a flat hook 

 capable of slipping into an arrangement on the 

 pinion block of the stand, is fastened to the upright 

 back of both. 



Grove's or Bunsen's elements are the best form of 

 battery ; bichromate cells from their inconstancy be- 

 ing a continual source of trouble. 



Magnesium in the form of Solomon's lamp may be 

 employed with low powers, when it is necessary to 

 shorten the exposure; but with high powers want of 

 light when focussing is the difficulty to be contended 

 with. The costliness of magnesium renders its pro- 

 longed use inapplicable to this purpose. 



Dr. Hayes has recently obtained excellent results 

 with the lime light by using an ordinary lantern with 

 4i inch condensers, the objective being removed and 

 a plano-convex lens substituted for it, about ten or 

 twelve inches in front of the lantern. This gives a i- 

 inch disc and is easily centred The same method 

 will obviously answer with the triplexicon or other 

 lamp. 



A minute intensely brilliant spot of light, requir- 



