NATURAL PHILOSOPHY. 161 







long;, having sufficient tension to pierce a piece of glass of one 

 centimetre thickness ; a tube more than a metre long, filled with 

 rarefied air, can be continuously illuminated, and combustibles at 

 a short distance set fire to. This plate can charge in 30 or 40 sec- 

 onds a battery of 2 metres (21 square feet) of interior surface, 

 which will volatilize a sheet of gold leaf, and burn a metre of 

 iron wire employed in the lightning arrester of telegraphs. In 

 the simplicity of its construction, this machine seems to realize 

 practically the idea of a continuous electrophorus, and of a con- 

 venient and permanent source of electricity. 



Ritchie's Modification. At the meeting of the Society of Arts 

 of the Massachusetts Institute of Technology, March 21, 1867, 

 Mr. E. S. Ritchie, of Boston, exhibited a new form of electrical 

 machine of his own construction, a modification of the machine 

 of Holtz, upon which, from its simplicity, it is believed to be a 

 great improvement. It is described iu the "Journal of the 

 Franklin Institute " for May, 1867. 



A strong plate of plate-glass is fixed in a vertical position upon 

 a mahogany frame, and sustains the bearing of one end of the 

 revolving shaft supported at its opposite end by a single pillar. 

 The revolving thin plate is fixed in the usual manner on its shaft 

 by a collar and binding nut of vulcanite, and is placed about one 

 inch distant from the thick plate. Four holes are drilled through 

 the thick plate at suitable distances from the centre, through 

 which pass the stems of the rods with points or combs ; balls of 

 metal or vulcanite screw against the opposite side and hold the 

 combs firmly in place ; the balls are connected with the discharg- 

 ing pillars. Four pairs of little pillars or bolts project from the 

 supporting plate in a circle surrounding the revolving plate, made 

 of vulcanite ; their outer ends are furnished with movable screw 

 shoulders and nuts. Upon each pair is placed one of the glass 

 sectors of the Holtz machine ; or, on alternate pairs, the rubber 

 sectors of the Bertsch arrangement. These pillars (the middle 

 one removable), with sliding discharging rods, furnished with 

 balls of different diameters and points, are connected by wires 

 (covered by insulating material, if desirable) to the balls of the 

 combs. Any desirecl combination can easily be made ; either of 

 the sectors or combs with its connections can at pleasure be re- 

 moved, or their distance from the revolving plate adjusted. The 

 relative positions of the parts-are held with great firmness. The 

 presence of the stationary plate, near the revolving one, adds to 

 its insulation, and, in this way, to the efficiency of the machine; 

 in other respects the advantages sought are simplicity and stabil- 

 ity. The insulation of the supporting plate allows the discharges 

 to be brought nearer the revolving plate, avoids disturbing influ- 

 ences from one to the other, and allows the machine to be much 

 more compact in form. 



The following are extracts from a letter from Mr. Ritchie to the 



^5 



editor of the " Journal," giving the results of some of his experi- 

 ments : 



" I removed the two upper sectors of my machine, leaving 2 at 90 

 degrees apart, thus leaving nearly three-fourths of the plate between 



14* 



