234 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The galvanometer was of the Thompson type and had a resistance 

 of 56.9 ohms, and a figure of merit of 2.3 X 410~*, with a scale 

 distance of 1 m. and scale divisions of 1 mm. The time of a half 

 vibration of tlie needle was 7 seconds. 



The bolometer resistances were attached to the under side of the 

 cover of a well made box of cherry (33 cm. long, 26 cm. wide, and 

 8 cm. deep). The resistances Wi and Wg were supported on 

 slender posts, so that they came nearly in the middle of the box, and 

 were equally exposed to the air on all sides. On the upper side of 

 the cover were the binding posts and sliding contacts. This box was 

 placed inside another one of similar construction (47 cm. long, 39 cm. 

 wide, and 23 cm. deep), and the space between was packed with 

 cotton wool. Cords from the sliding contacts were led through the 

 sides of the outer box, so that adjustments of the arms could be made 

 without exposing or touching the bolometer. Even with this pro- 

 tection from thermal changes, much difficulty was experienced when 

 the hot weather came, and the temperature of the room could not be 

 kept constant. It was found, however, that early in the morning very 

 little disturbance was experienced, and most of the observations 

 whose results are reported were recorded before the heat of the 

 morning was much felt in the room containing the bolometer. 



To use the bolometer for measuring the energy at all places on the 

 wires forming the secondary circuit, the arrangement devised by 

 Rubens* was used. Over the two wires KL and M N (Fig. 5), 

 were slipped thick-walled capillary tubes of glass, about 5 cm. long, 

 and these were held by a small wooden bar, so that they could be 

 slipped along together. This arrangement is spoken of hereafter as 

 the exploring terminals. The ends of the lead-wires to the bolometer 

 were wound once around the tubes and fastened by sealing wax. 

 These formed two Leyden jars of extremely small capacity, and 

 the oscillations of charge on their inner coatings, which were formed 

 by the wires KL and MN, produced rapidly oscillating currents 

 through the bolometer resistance Wo. For leading wires to the bolom- 

 eter silk covered copper wire No. 36 was used that had been drawn 

 through hot paraffine. Larger wires were tried and wires with rubber 

 insulation, but with these the apparatus was less sensitive. 



The following method was pursued in taking the observations. 

 The interruptor was set in action, the circuit closed through the 

 induction coil, and an observation taken of the first swing of the 



* Ueber stehendc electrische Wellen in Draliten und deren Messungen. 

 Poggendorff, Annak'n, XLII. 154 



