152 Scientific Intelligence. 



in a vacuum. The dispersion in silver is however not great. The 

 velocity in gold and copper is also greater than in a vacuum, and 

 the dispersion normal. In other metals the dispersion was found 

 to be abnormal. The theoretical conclusions of Beer and Yoigt 

 in so far agree with the results of Kundt to a remarkable degree. 

 If we call the velocity of light in silver 100, we have the fol- 

 lowing : 



Silver. Gold. Copper. Platinum. Iron. Nickel. Bismuth. 

 100 71 60 15-3 14-9 12 -4 10*3 



"With the exception of bismuth, this series is the same as that 

 of the electrical resistance of metals. The number for copper 

 however is somewhat small and may be due to impurity. The 

 ratio of the heat conduction and electrical resistance of bismuth 

 is still in question. From the above numbers one is tempted to 

 conclude that the electrical resistance is proportional to the 

 velocity of light of great wave length. We have here a relation 

 between electricity — conduction of heat and velocity of light — 

 Kundt is tempted to believe that the slowness of heat conduction 

 in metals is due to the radiation from one layer to the adjoining, 

 whereas the radiation itself in metals has the velocity of light. 

 What we call electricity moves in a conductor with the velocity 

 of light.— Ann. der Physih unci Ghemie, pp. 469-489, No. 7, 1888. 



J. T. 



3. Resistance of square bars to Torsion. — T. I. Dewar calls 

 attention to an error which has crept into various articles, including 

 Prof. Ewing's on the Steam Engine in the Encyclopaedia Brittanica, 

 Sir William Thomson's article on elasticity in the same encyclopae- 

 dia, Thomson and Tait's Natural Philosophy, and Minchen's Statics. 

 The moment of resistance of a square bar to torsion is given by 

 Saint Yenant as 0-281 /A 3 where /=maximun intensity of stress 

 and A = side of square. Saint Yenant gives the correct formula 

 afterward as 0-208 fh*. " It seems strange that the talented 

 author of the expressive distinctions, strain and stress, should him- 

 self have taken the formula for the strain instead of that for the 

 stress." At the time he wrote however strain and stress were sup- 

 posed to be proportional to each other. — Nature, p. 126, June 7, 

 1888. J. T. 



4. Latent heat of evaporation of Water. — Regnault's experi- 

 ments were made at temperatures above 0° and he obtained a form- 

 ula which led to the value 607 units of heat, the latent heat of 

 evaporation at 0°. Dr. Dieterici, by the use of an ice calorimeter 

 has made a direct determination of tins constant, and has obtained 

 the value 596*4 thermal units at 0°. — Nature, p. 143, June 7, 1888. 



J. T. 



5. Electrolysis by alternating currents of Electricity. — M.M. 

 Maxeuvrier and J. Chappuis show that the size of the elec- 

 trodes exercises a great influence in the electrolysis by alternat- 

 ing currents. With currents of 250 to 300 volts and 4 to 5 Am- 

 peres, no trace of electrolysis can be discovered with electrodes 

 of 0'l cm in diameter and 4 em to 5 cm in length. If one however sub- 



