xlvi GENERAL SUMMARY OF SCIENTIFIC AND 



centre of the diaphragm by the elastic force of four carefully tem- 

 pered steel springs which is independent of any variation of 

 gravity. Being open to the atmosphere both above and below, the in- 

 strument is unaffected by variations in the pressure of the air. The 

 peculiar form of the column was given to it in order to render the 

 instrument parathermal, or independent of temperature. The read- 

 ing is effected either by electric contact or by means of a spiral 

 graduated tube fixed on the top of the instrument, and communi- 

 cating with the space above the mercury, which contains a liquid 

 of less density partially filling the tube. The graduations are em- 

 pirical, since this is much easier than calculation. Experiments in 

 the Faraday with Sir William Thomson's sounding-line gave 82 

 fathoms at 12, 204 fathoms at 1.08 P.M., and 69 fathoms at 2.20 ; 

 the bathometer showed 82,218, and 78. 



In Mechanics^ Kimball has published the results of some experi- 

 ments made by him to ascertain whether the coefiicient of sliding 

 friction is constant at all velocities, as it is ordinarily stated to be, or 

 whether it varies inversely as the velocity, as certain practical results 

 seem to render probable. The figures given show : (1) that with a 

 given inclination of the plane, the coefficient of friction decreases 

 as the velocity increases, rapidly at first, but more slowly after- 

 ward ; (2) with the same velocity, the coefficient of friction is great- 

 er the greater the inclination of the plane, within the limits of the 

 exjieriments ; (3) that the coefiicient of friction in each experiment 

 tends toward a constant quantity ; and (4) this constant seems to be 

 the same in each experiment. 



The same physicist has studied the changes produced in the 

 physical properties of steel by tempering. He finds (1) that the 

 modulus of elasticity decreases as the hardness of the steel increases ; 

 (2) that the increase of defiection in a given time is greater the 

 harder the steel ; (3) that the immediate set increases with the 

 hardness of the steel ; and (4) that a bar recovers from a temporary 

 set with greater rapidity the harder it is. 



The process of M. De la Bastie for hardening glass has met with 

 a formidable rival. F. Siemens, the well-known Dresden manufact- 

 urer, has patented a method of hardening, tempering, and j^ress- 

 ing glass all at the same time. Instead of plunging the softened 

 glass in a bath of cold oil, the molten glass is run into suitable 

 moulds, and while still highly heated is squeezed, the moulds 

 which are generally of metal having the effect of giving the nec- 

 essary cooling. For blown glass, shells or casings of platinum are 

 made, and these are transferred to the mould together with the 

 glass. 



Lawrence Smith has devised a simple form of compensating pen- 

 dulum, founded on the considerable expansibility of hard rubber or 

 vulcanite by heat. The seconds pendulum he uses consists of a 



