XXVI 



INTRODUCTION. 



rest, the tangent screw to the circle was turned until the image of the central division of the 

 scale (300.0) was covered by the telescope wire. The verniers were then read and magnet 

 No. 2x 3.67 inches was placed on the supports within the box. Turning the instrument 

 through an angle precisely equal to the deflection produced, the circle verniers were again read, 

 at which instant the scale of the vibration apparatus, set up within thirty feet to determine 

 changes of declination, denoted 296.0. 



CIRCLE READINGS. 



Before temperature experiments. 



Magnet away. Magnet in place. 



After temperature experiments. 



Magnet in place. 



245 29 10 

 30 00 



27 20 



229 38 10 

 39 00 

 36 20 



Magnet away. 

 o ' " 



245 30 50 

 31 30 

 28 50 



239 42 40 

 43 10 

 40 20 



After the first readings of the circle, a thermometer was placed in the box with its bulb near 

 the magnet, and the box carefully filled with warm water. When it was thought that the 

 box, water, and magnet, were of the same temperature, five simultaneous readings of the ther- 

 mometer, the unifilar, and the declinometer scales, were made at equal intervals of time. The 

 hot water was next drawn off with a syphon and ice-water substituted, whose temperature and 

 influence on the deflector were noted in the same manner. A repetition of both hot and cold 

 water trials followed, with the results shown in the subjoined table. Pounded ice was used in 

 reducing the temperature of the cold water. At the last reading with the (deflector) "magnet 

 in place," the magnet and interior of the box were both still wet. 



Experiments for temperature coefficient of magnet No. 2x 3.6*7 inches. 



