720 Transactions of the American Institute. 



feet six inches apart, the principal part of the driving machinery heing 

 between. • The hind wheels nm close together and oveHap a little, so 

 that the total width covered is seven feet six inches. Power is com- 

 municated to tlie front wlieels by an improved endless chain of great 

 strength. The machine is steered by means of the hind wheels, which 

 are fitted in a turntable ; it can be turned around with great ease 

 within a circle tiiirty feet in diameter, but as the rollers work equally 

 well in moving backward or forward, it is seldom necessary to turn 

 the machine. It weiglis twenty-five tons, and was purchased from 

 Messrs. Aveling and Portern, London, at a cost of $4,500. After 

 passing two or three times over a rough and almost impassable 

 thoroughfare, the machine converted it into a smooth and level road. 

 A similar engine, but much heavier, is in successful operation at 

 Liverpool. 



A ISTovEL Thermometer. 



Dr. J. P. Joule has constructed a thermometer oh a new principle. 

 It consists of a copper tube surrounding another tube having a hinged 

 bottom. Within the smaller tube which is open at the top, is a fine 

 wire having a spiral form and suspended by a silk thread, upon 

 which a small mirror is fastened so as to turn with the thread. When 

 the bottom is closed, the mirror reflects a light, so as to mark zero on 

 a graduated scale ; but when open, the air inside the tube being 

 warmer than that outside of the apparatus, a current is established 

 which, by means of the spiral wire, twists the silk thread. A 

 difference of one degree Fahrenheit between the inside and outside 

 air produces a current sufficient to cause a complete tui-n of the 

 thread. The elevation of temperature within the tube is, according 

 to the views of the author, produced by the absorption of heat by 

 the copper tube, which is radiated internany. It is evident this 

 apparatus cannot be used out of doors on n windy day, or e%'en in a 

 room in which currents of air are moving. 



Differential Saturometer. 

 This instrument, invented and lately patented by M. Coret, is an 

 attachment to the boilers of steamships in which steam is made from 

 seawater, intended to indicate the degree of saturation, and at the 

 same time record the level of the water in the boiler. The action of 

 the instrument depends on the well-known principle that when two 

 different liquids, having the same temperature and no chemical 

 affinity, are placed in an inverted syphon, their heights in each 



