physics. 587 



Laurie has shown that if the atomic weights of the elements are taken 

 as abscissas and their atomic heats of combination with chlorine as ordi- 

 nates of a curve, the heats of combination will be seen to be a periodic 

 function of the atomic weights. (Phil. Mag., January, 18.S3, V, xv, 42.) 



Crafts has made use of hydrogen in his thermometers, because of the 

 facility of flowing most rapidly through capillary tubes. The volume 

 of the reservoir is small, only from one to ten cubic centimeters. The 

 instrument is used at constant volume, an electric contact between the 

 mercury of the manometer and a platinum point being established when 

 the gas reaches the fixed volume, thus exciting an electro-magnet aud 

 closing the manometer cock. (J. Phijs., September, 1883, II, n, 435.) 



Dufour has contrived an ingenious form of differential thermometer, 

 which is especially useful for purposes of demonstration. Two bulbs of 

 15 or 20 millimeters in diameter close the ends of a glass tube forming 

 the segment of a circle. The tube contains a drop of mercury, and the 

 whole is supported upon a knife edge, slightly above its center of gravity, 

 the position of which may be altered by a counter- weight. An index 

 passes vertically upward and moves over a graduated arc. When the 

 two bulbs are of the same temperature, the system is horizontal and 

 the index vertical. But if the temperature of one of the bulbs rises, the 

 expansion of the air drives the mercury to one side and the tube inclines 

 to one side. If one of the bulbs is blackened and the other gilded, the 

 apparatus serves well for experiments on radiant heat, especially if a 

 cone be employed to concentrate the heat upon the blackened bulb 

 (Jovr. Phys., July, 1883, II, n, 321.) 



Negretta and Zambra have adapted their inverting thermometer for 

 lecording variations of atmospheric temperature at any desired interval 

 of time. Twelve such thermometers are arranged on a suitable frame, 

 in connection with a clock, a galvanic battery, and a series of small 

 electro-magnets, in such a way that at every hour the circuit is com- 

 pleted by the clock, thus releasing a detent and allowing one of the 

 thermometers to reverse and record the temperature at that moment. 

 In the present form of the apparatus, the twelve thermometers have 

 been mounted to record hourly temperatures; but the period can ob- 

 A T iously be lengthened or shortened indefinitely. The advantages 

 claimed for the system are: 1st, the thermometers contain only mercury, 

 without any alcohol or other liquid ; 2d, they have neither indices nor 

 springs, the column of mercury itself effecting the registrations; 3d, 

 they may be carried in any position, and cannot be disarranged except 

 by actual breakage; and, 4th, they will record exact temperature at 

 any hour of the day or night. (Nature, July, 1883, xxviii, 306.) 



Nicol has described a form of constant- temperature bath, in which 

 the extreme variation of temperature does not exceed 0.05°. The water 

 in the bath is heated by the circulation of other water in a copper tube, 

 which passes through the flame of a Bunsen burner, the supply of gas 

 being controlled by a suitable thermometer placed in the liquid, being 



