NATURAL PHILOSOPHY. 149 



coincident with the sun in its progress produced the variations of the 

 perpendicular ill the Monument. The extreme departure of the ball 

 from the centre was to the west of north-west ; not to the north, as 

 might at first glance be supposed. The explanation is found in the 

 position of the Monument. Its sides do not face the cardinal points, 

 but are inclined about 20. The expansion of a single side would pro- 

 duce inclination in a direction perpendicular to the side. The expan- 

 sion of two adjacent sides would produce inclination in the direction of 

 the diagonal. In the morning the shaft is inclined to the westward. 

 At noon it is inclined but little to the north of west. In the progress 

 of the afternoon, it sweeps over twice the amount of movement in the 

 morning ; describing, in the twelve hours of observation, an arc of an 

 ellipse. During the night it sets back to the centre, and before seven 

 o'clock in the morning has already moved westward. The greatest 

 diameter of the irregular ellipse, described by the index in twenty-four 

 hours, is ordinarily less than half an inch, while the least was less than 

 a quarter of an inch. The heat of the sun penetrates to but a moder- 

 ate depth. This is evident from the prompt movement of the column 

 when a shower falls only upon the more highly heated sides, and also 

 from the ready change in inclination as the day advances. 



The mode of observation at the Monument is this : On either side, 

 about three quarters of an inch from the centre, under the index of the 

 ball, two slender needles have been driven into the floor, leaving not 

 more than the sixteenth of an inch above. These are made by pres- 

 sure to pierce a card of thin drawing-paper, which is kept from warp- 

 ing by slender bars of lead. When fixed, north and south and east 

 and west lines are transferred in pencil mark from the floor to the 

 paper. After bringing the ball to rest, in which the observer is aided 

 by a contrivance enabling him to steady his hands, a dot is made with 

 a pencil immediately under the index-point, which is about the six- 

 teenth of an inch above the paper. At the close of the day, the card 

 previously dated is removed, and another takes its place for the obser- 

 vations of the next day. Prof. Horsford, American Association, Al- 

 bany Meeting. 



LATENT HEAT IN ICE. 



PERDON has determined the latent heat of fusion of ice, at C., 

 and at lower temperatures, and has ascertained that in order to obtain 

 the total quantity of heat which is absorbed when ice becomes liquid, 

 it is necessary to set out from a temperature somewhat below 0. The 

 experiments were made by means of a calorimeter, founded on the 

 method of mixtures. The loss of heat by radiation was compen- 

 sated by placing the calorimeter in a space, the temperature of which 

 could be made to follow that of the calorimeter itself, and the method 

 was verified by determinations of the specific heat of water at different 

 temperatures, which agree well with those of Regnault. The author 

 first determined the specific heat of ice between 21 C. and 2 C., em- 

 ploying in the calorimeter a solution of salt, the specific heat of which 

 had been previously determined. The specific heat of ice. between 



13* 



