474 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



meters high inside, 45 centimeters wide, and 22 centimeters deep' (Fig- 

 ure 1), serves to support three vertical rods or columns made of straight 



round steel shafting 3.8 centimeters 

 in diameter held at top and bottom 

 in iron castings. On the middle 

 column slides smoothly a cylindrical 

 iron weight Q which can be caught 

 and held at any convenient height by 

 a latch K which can be slipped from 

 a distance by a string. The weight 

 as it falls can be made to trip in 

 succession a number of switches sup- 

 ported on the other columns, and thus 

 to open or close a a series of circuits 

 at definite intervals. A dash pot N 

 at the bottom of the middle column 

 catches the falling weight. 



In the early experiments made 

 with this apparatus the falling 

 weight was used to close in succes- 

 sion three keys. The first completed 

 the charging circuit so that both 

 condensers were charged to the same 

 potential, usually 64 volts, the second 

 discharged the condensers against 

 each other, and the third put both 

 condensers, still opposed, in circuit 

 with a d' Arson val galvanometer. 

 For most of the work, however, the 

 falling weight was equipped with six 

 knife edges at the ends of short 

 horizontal steel rods projecting, two 

 towards the north, two towards the 

 south, and two towards the front 

 (east) of the apparatus. The last 

 pair were insulated from the iron. 

 These knives ploughed furrows in 

 " type metal pieces held in elaborate 

 brass clamps mounted on the outer 

 columns of the machine, but the south 

 furrows were less than a millimeter long, while the east and the north 

 furrows were 19 millimeters and 22 millimeters long respectively. 



Figure 1. 



