Polytechnic Association Proceedings, 555 



tubes. This material will be turned to stone long before the iron 

 inclosing it can waste away by oxidation. 



THE GAIN OF CARBUEETTED GAS. 



The process of passing ordinary coal gas through a volatile 

 hydrocarbon, for the purpose of increasing its illuminating power, 

 recently introduced both in this country and Europe, seems to be 

 quite generally approved. Once a Week, in a late number, says the 

 advantage of the process is not confined to the increased light, but 

 there is less vitiated air and less heat engendered by the combus- 

 tion of carburetted, than of common gas — always providmg that 

 proper care be taken, by the use of suitable jets, to insure the per- 

 fect combustion of all the gas that issues from the burners. With- 

 out such provision any gas, carburetted or not, will smoke or give 

 off noxious vapors. As evidence of the perfect working of the 

 invention, that journal cites, upon the authority of the manufac- 

 turers, that several thousand of these carburettors have been sup- 

 plied to various consumers, large and small, since its introduction, 

 and that these have been maintained in continual use, without 

 trouble and without detriment. Some of the street lamps at the 

 West-end of London are, at the present time, burning " carburetted" 

 gas — the lamps around Trafalgar square, to wit — and several of the 

 public offices in London likewise adopt the carburetting principle. 



VIBRATION ILLUSTRATED. 



Prof. Tyndall, of the Roj^al Institution of London, has arranged 

 an apparatus for representing to the eye, on a large screen, the 

 vibratory action of solids producing various musical tones. In this 

 way he demonstrates that a string has, besides its general vibratory 

 movements, segmental vibrations, between which are nodes or 

 points of rest. In one case a rod was held in a vise in such a way 

 that, by means of a strong light, its shadow could be thrown upon 

 a screen; on being struck sharply at certain points it was made to 

 divide itself into two or more vibrating seofments and half see:- 

 ments, the former showing themselves as shadowy spindles, the 

 latter, as fans upon the screen. The nodes were designated by 

 dark points of stationary shadow. 



In another case, a tuning fork was connected with a fine pla- 

 tinum wire, heated by a galvanic current. When the fork gave 

 forth a sound, the hot platinum wire responded to the vibration, 

 and, its middle portion swinging through the great arc, was soon 

 cooled. On being slackened, the wire resolved itself into tvro or 



