PHYSICS. 253 



a coin, it will be held there owing to the elasticity of the glass. On 

 warming now the outer surface of the glass it expands and the coin drops 

 out. LeConte, apropos of this, gives an equally striking method for 

 showing the same thing, first observed by Orme in 1740. A straight 

 glass tube, 50 or GO*"'" in length and one or two in diameter, is placed 

 transversely before the fire, supported horizontally near its two ends on 

 rods of hard wood of about the same diameter, c^irefully Icn-elcd. It 

 will now roll toward the fire. If the supporting rods be transferred in- 

 ward so as to support the tube near its middle, the tube will gradually 

 roW from the fire. In this case the expansion of the glass by the heat is 

 the moving cause, the falling of the side thus made convex producing 

 the motion. — {Phil. Mag., June, 1880; Nature, xxii, 157, 318, 1880.) 



Yillari has experimented to determine the law of the production of 

 heat by the electric spark in gases. He used a glass globe of about a 

 liter capacity, having two horizontal and two vertical tubulures. ]>y the 

 former, the electrodes entered the globe ; the upper vertical one carried 

 a stopcock, and the lower a tube plunged in a diluted glycerin, serving 

 as a thermometer. Care was taken to protect the globe from loss or 

 gain of heat. The results are given in three laws : 1st, the heat devel- 

 oped by the electric spark in gases is directly proportional to the quan- 

 tity of electricity which produces it ; 2d, the quantity of heat developed 

 by the electric spark increases in the proportion of its length ; 3d, the 

 heat and also the galvanometric deviations produced by the discharge 

 of a condenser are independent of its surface. The result was not af- 

 fected by the direction of the spark. — {J. Phys.. ix, 5, January, 1880.) 



Barrett has studied the phenomena presented by the Trevelyan rocker, 

 and has come to the conclusion that the theory which ascribes the mo- 

 tion to the rapid expansion and contraction of the metals in contact is 

 not the correct one. He believes this motion to be due to the action of 

 a polarized layer of gas between the hot and cold surfiices, like that ex- 

 isting between the hot and cold surfaces of the layer of vapor support- 

 ing a drop of liquid in the spheroidal state, termed by Stoney a " Crookes 

 \2iyQv:^— {Nature, xxi, 426, March, 1880.) 



Carnelley, from certain of his experiments, concluded that in order to 

 convert a solid into a liquid, the pressure must be above a certain point, 

 which he calls the "critical pressure" of the substance, otherwise no 

 amount of heat will melt the substance ; just as in converting a gas into a 

 liquid the temperature must be below the critical temperature, or no 

 amount of pressure will liquefy the gas. As a deduction from his law, it 

 follows that, provided the pressure be below the critical pressure, solid 

 ice may be heated to temperatures far above its melting point, passing 

 then directly into the gaseous condition without previously liquefying. 

 He therefore tried the experiment, and he succeeded in obtaining "solid 

 ice at temi)eratures so high that it was impossible to touch it without 

 burning one's self." Not only so, but water has been frozen in a glass 

 vessel which was so hot that it could not be touched by the hand with- 



