436 SCIENTIFIC RECORD FOR 1884. 



F. J. Siiitli has described a new transmitting dynamometer or ergom- 

 eter, as he calls it, which resembles the early dynamometer of ^Morin 

 in having two pulleys, the angular advance of one being regulated by 

 a spring. In the Morin instrument, however, an extended piece of steel 

 formed the spring; and in the modified form of it proposed by Ayrton 

 and Perry spiral springs were used. In the latter form the springs are 

 liable to fly out by centrifugal force, and, moreover, a special optical 

 arrangement is required for reading the angular advance. In Smith's 

 ergometer there is no tendency in the spring to fly, and the tension is 

 read directly upon a dial. {Nature, July, 1884, xxx, 220.) 



Brackett has devised a dynamometer especially adapted for measur- 

 ing the energy expended on a dynamo-machine. The machine to be 

 tested is so supported that it can turn freely through a small arc of a 

 circle, the center of which is in the armature axis. When the armature 

 is rotated, the circuit being closed, a mechanical couple is set up be- 

 tween this armature and the field maguets, which tends to make the 

 latter revolve in the same direction as the ajjjnature. The value of this 

 couple is ascertained by measuring the value of the equal and opposite 

 couple required to maintain equilibrium. This is done by means of a 

 lever-arm fixed to the machine or cradle, provided with a sliding weight 

 sufficient to maintain the machine at zero. The length of the lever- arm 

 and weight being known, it is necessary to know only the number of 

 revolutions in order to calculate the energy. If W denote the weight, 

 L the lever-arm, and n the number of revolutions in a minute, the en- 

 ergy expended will be represented by 27:LWw. {Am. J. Sci., January, 

 1884, III, XXVII, 20.) 



Boltzmann, by means of Carnot's principle and the theory of proba 

 biiities, has calculated the energy developed in chemical combination, 

 considering only the cases where the substances are gaseous both before 

 and after the reaction, and where the diatomic molecules dissociate into 

 atoms of the same kind. Assuming that the heat of dissociation is in- 

 dependent of the temperature, the formula gives as the number of ca- 

 lories (gram-degrees) required for the dissociation of one gram of nitro- 

 gen tetroxide, 151.3 ; and of iodine vapor, 112.5. {Ber. AJ{. Wien, 1884, 

 181; J. Phys., II, ill, 274, June, 1884.) 



Sir William Thomson described at Montreal a gyrostatic balance for 

 measuring the vertical component of the earth's rotation, which con- 

 sisted of a gyrostat supported on knife-edges attached to its contaiuing- 

 case, with their line perpendicular to the axis of the interior fly- wheel, 

 and above the center of gravity of the fly-wheel and frame- work, by an 

 exceedingly small height when the frame- work is held with the axis of 

 the fly-wheel and the line of the knife-edges both horizontal, and the 

 knife-edges downward in proper position for performing their function. 

 The apparatus, when supported on its knife-edges, with the fly-wheel 

 not spinning, may be dealt with as the beam of an ordinnry balance. 

 Let now the frame- work bear iwo small knife-edges or knife-edged holes, 

 like those of the beam of au ordinary balance, giving bearing-points 



