TRANSACTIONS OF SECTION A. 



477 



experiments were conducted, and also to Mr. Gore, F.R.S., for the loan of a longer 

 bar of nickel. Experiments are now in progress to determine the eilect of tempe- 

 ratures and longitudinal tension on the results.* 



4. On an Instrument for measuring tlie Intensity of Aerial Vihratiun.- By 

 Professor Lord Eayleigh, F.B.S. 



5. On the Effect of Wind on the DraugJd of Chimneys. By Professor 



Lord Rayleigh, F.B.S. 



6. On a Mechanical Self-registering Thermometer. By A. Mallock. 



Having recently had occasion to keep a room at a constant temperature for 

 many days together, the author had, in order to test the efficiency of the apparatus 

 employed for that purpose, to have some means of continuously recording the 

 temperature of the room and also of the external air. 



Several causes prevented the use of the ordinary photographic method, and he 

 therefore designed the mechanical recording thermometer which is the subject of 

 this communication ; and since there are obvious advantages in dispensing with 

 photography if equally accurate results can be obtained by a simple mechanical 

 means, and as the same principles can be applied to the construction of a me- 

 chanical self-recording barometer, he hopes the short description of his apparatus, 

 which will be given here, may not be without some use. 



The thermometer consists of a long glass bidb (A) holding about half a pint of 

 spirits of wine. This bulb is connected by a fine metallic tube (B), also full of spirit, 

 with a small bulb (C) near the recording apparatus. is half-full of mercury 

 and half of spirit, and terminates in a capillary tube (D), which dips into a deep 



cup (E), which also contains mercury. This cup is suspended from a horizontal 

 lever (F), and its weight, without the mercury, coimterbalanced. 



The weight of the mercury in the cup is talreu by the spiral spring (G). 



The upright arm (H), attached to the lever, carries the pen-rod (K), which 

 marks on the horizontal cylinder (L). 



The cylinder turns round once a week, and time is marked on the paper at 

 intervals of three hours by a pen (M) actuated by an electro-magnet through 

 which currents are sent at the desired intervals by a contact-maker on the clock. 



The effect of a change of temperatui-e is to expel or suck mercury from or into 

 the small bulb, and the variation of weight on the spiral spring is'the same as it 

 would have been had the large bulbs been filled with mercury, and mercury had 

 the coefficient of expansion of spirits of wine. 



* For a fuller report of this paper, see the Electrician for October 14, 1882. 

 2 Phil. May. September, 1882. 



