PHYSICS. 



By George F. Barker, 



Professor of Physics in the University of Pennsylvania, Philadelphia. 



GENERAL. 



The progress of physical science for the year 1883 has been very con- 

 siderable, especially in the department of electricity. This advance, 

 however, has been made chiefly in the applications of known electrical 

 principles, rather than in the discover}' of new ones. 



In a lecture before the Royal Institution, Sir William Thomson has 

 discussed the " size of atoms," using the terms atom and molecule 

 synonymously. He takes the broad view that matter, though we may 

 conceive it to be infinitely divisible, is not infinitely divisible without 

 decomposition; and hence that the question whether we can divide a 

 piece of glass into pieces smaller than the 1-100,000 of a centimeter in 

 diameter, and so on, without breaking it up and making it cease to have 

 the properties of glass, just as a brick has not the properties of a brick 

 wall, is a very practical one. As the result of four independent lines of 

 argument, the molecules of ordinary matter would seem to be from the 

 1-10,000,000 to the 1-100,000,000 of a centimeter in diameter. These 

 four lines of reasoning are founded respectively on the undulatory 

 theory of light, on the phenomena of contact electricity, on capillary at- 

 traction, and on the kinetic theory of gases, the lecture being devoted 

 to their development. (Nature, June, July, 1883, xxvin, 203, 250, 274.) 



Reinold and Biicker have communicated to the Royal Society the 

 results of their investigation of liquid films, measuring the thickness 

 of such fi'ms when so thin as to exhibit the black of the first order of 

 Newton's rings. They used two methods for this purpose; one, based 

 on a determination of the electrical resistance of a cylindrical black 

 soap-film, the thickness being calculated by means of Ohm's law; and 

 the other an optical method, depending upon the displacement of inter- 

 ference fringes when one of the interfering beams traversed several 

 films which were afterward broken. The mean of the electrical measure- 

 ments gave a thickness of 11.8 xl0~ 6 millimeters; that of the optical 

 method, one of 11.4xlO _G millimeters. These results are of interest 



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