INDUSTRIAL PROGRESS DURING THE YEAR 1874. x \\ 



coveries may at last be found that " agent acting constantly- 

 according to certain laws" which Newton holds to be the 

 cause of gravitation. The observations of Crookes have, on 

 the one hand, called forth a criticism by Reynolds, showing 

 that the evaporation of minute portions of vapor will par- 

 tially explain them, and, on the other hand, have elicited from 

 Professor Crookes a reply, in which he adduces still further 

 and crucial experiments, maintaining his original proposi- 

 tions. 



Professor Tresca has observed, during the forging of the 

 great ingot of platino-iridium, that one could see upon its 

 sides luminous streaks accompanying each blow of the ham- 

 mer, and he shows that the zone which becomes momentarily 

 luminous in consequence of the blows of the hammer is that 

 along which the molecules flow when the change of form 

 takes place consequent upon the blow. 



Fatigati has made a new determination of the mechanical 

 equivalent of heat through the medium of electricity, and his 

 result (464.87 units of work) agrees well with that ordina- 

 rily received. 



The laws of the explosion of gases within fire-arms have 

 been deduced by Sarran from well-known laws of chemistry 

 and thermo-dynamics. He considers that his results are re- 

 markably confirmed by observations made by the French 

 Naval Artillery Commission. Messrs. Abel and Nobel have 

 published the accurate results of their observations on the 

 explosion of gunpowder. They find the temperature at the 

 moment of explosion to be about 2200 C, and the tension of 

 the confined gases 41.7 tons to the square inch. 



In Optics, Professor Pickering has made an excellent and 

 very elaborate research on the polarization of the light re- 

 flected from the sky and from one or more plates of glass. 



The fact that the zodiacal light is polarized in a plane 

 passing through the sun has been first established this year 

 by Professor A. W. Wright. This fact seems to show that 

 the zodiacal light is the sun's light reflected from innumera- 

 ble small meteoric bodies. Professor Wright found that fif- 

 teen per cent, of this light is polarized. He has also made 

 careful examinations of the spectrum of the zodiacal light, 

 and his results conform to the hypothesis above advanced 

 as to the origin of this light. 



