228 PROCEEDINGS OF THE AMERICAN ACADEMY 



set in motion the wheel P, and the regulating parts r, r', which are 

 attached; the chain /t', which moves the carbon-holder of the positive 

 pole, rolling up on the groove of //, will make the carbon C ascend, 

 while the chain h, unrolling from about the groove of /j, will make 

 the corresponding carbon C descend. The ratio of the diameter of 

 the pulleys p, p' can be changed by a special system of elastic pres- 

 sures belonging to the groove p of the pulley of the negative pole, 

 and which is represented on a large scale in Figure 2. By the help 

 of a key, any dimension wished is given to the pulley p. This dimen- 

 sion must always be such that the point of contact of the two carbons 

 shall be maintained at the same elevation, in spite of the more rapid waste 

 of the positive pole. Now the quantity by which the negative carbon 

 descends, and that by which the positive carbon mounts, are propor- 

 tioned to the circumferences of the respective pulleys, and these cir- 

 cumferences are in the same ratio as their diameters. If the positive 

 carbon is wasted three times more rapidly than the negative carbon, 

 the pulleys' must have three times as large a diameter as the pulley 

 p, in order to maintain the point of junction at a constant level. The 

 ratio of the diameter of the two pulleys must be regulated by trial 

 every time the carbons are changed, since a difference in their diame- 

 ters or their densities may cause a great difference in the waste of 

 the two incandescent extremities. The contact-maker K is provided 

 with a driving-screw, so as to alter at will its distance from the electro- 

 magnet, according to the energy of the pile used, which struggles 

 with more or less force against the spring s, which resists contact. 

 The place at which it is best to stop the contact-maker K is easily 

 discovered by a hissing which is produced when the carbons are too 

 near. This screw is so turned as first to provoke this hissing, and 

 then turned gently in the opposite dii'ection until the noise ceases. 

 The proper place for experiment is where the hissing stops. If with- 

 in or without this position, the carbons are too near or too distant. 



" The tube of the negative carbon is provided at n with a nut or an 

 articulated knee, by which there can be impressed upon it, with the 

 aid of the buttoned stem m, a slight conical movement around the 

 vertical, so as always to make its point coincide exactly with that 

 of the positive carbon. After one or two experiments with this appa- 

 ratus, the play of its parts presents no longer any serious difficulty, 

 and its manipulation becomes as simple as that of the Carcel lamp, or 

 the ordinary lampc a modcrateur.'''' 



