ELECTRICAL APPARATUS. 255 



observed to increase rapidly. The cylinder must next be 

 wiped perfectly clean with an old silk handkerchief, and 

 afterwards with a soft dry linen cloth. Let the cushion be 

 again removed, and the amalgam which appears above and 

 below the line of contact with the cylinder carefully scraped 

 off, the silk flap wiped with the linen cloth, and the whole 

 returned to its place and made fast. If now the cylinder be 

 turned slowly round, streams of the electric fluid will be 

 seen rushing from the silk flap round the lower pan of the 

 cylinder, attended with a hissing and snapping noise, while 

 large brushes of the same, of several inches in length, may 

 be observed flying off from the lower edge of the silk into 

 the surrounding air. The machine is now fit for use, and 

 may be fastened to the table ; after which the whole of its 

 parts are to be well wiped with a warm and dry linen cloth, 

 to free them from dust. 



The operator, however, must not expect this high and 

 rich state of excitation to be of long duration. The cylinder 

 will soon cool ; dust will be attracted by the action of the 

 machine ; and the moisture produced in the air of the room 

 by the breaths of his audience, will, by their united effects, 

 render all his efforts to produce a copious supply of elec- 

 tricity entirely fruitless. 



To remedy this defect, which gentlemen who deliver 

 public lectures on electricity have often found to be a griev- 

 ous one, and surround it with a dry atmosphere entirely 

 preventing the deposition of the moisture of the room from 

 settling on the machine, provide a box of thin plate iron, ten 

 or twelve inches long, four inches wide, and one inch and a 

 half in depth, with a lid to fit very easily over it. In this 

 box a piece of bar iron, of about six inches in length, three 

 in breadth, and half an inch in thickness, after being heated 

 in the fire to a dull red heat, is to be placed, the lid of the 

 box put on, and the whole, on a suitable iron stand, placed 

 under the cylinder, on the board of the machine, in a longi- 

 tudinal direction. The radiation of heat from the iron will 

 effectually preserve the equality of the temperature of the 

 surrounding air for a considerable length of time, and in- 

 deed for any length of time required, since, by employing 

 two bars of iron, the one may be kept in the fire, while the 

 other is in the box, and thus no other interruption in the 

 course of the experiments will be necessary beyond what is 

 occasioned by the changing of the irons. By this means 



