452 SCIENTIFIC RECORD FOR 1884. 



by meaus of a rectangular trougli having a curved bottom, lined on the 

 inside with polished plates, so arranged that they reflect the sun's rays 

 towards a cylindrical boiler placed lougitudinally above the trough. 

 The trough is 11 feet long and 16 broad, and receives a beam of sun- 

 light of 23,400 square inches in section. The boiler is 6^ inches in 

 diameter and 11 feet long. The motor employed is a steam-engine 

 with a cylinder 6 inches in diameter and 8 inches stroke. In the trials 

 the previous summer the average speed of the engine was 120 turns a 

 minute, the pressure on the piston being 35 pounds per square inch. 

 From these results, Ericsson deduces some conclusions with reference 

 the solar temperature. The area of a sphere whose radius is equal to 

 the earth's mean distance from the sun being to the area of the latter 

 as 214.5^ : 1, while the reflector of the solar motor intercepts a sun- 

 beam of 23,400 square inches section, it follows that the reflector will 



receive the heat developed by* ^ ', ^, = 0.508 square inch of the solar 



214.5^ 



surface. Hence, as the boiler of the motor contains 1,274 square inches, 



the solar rays acting on it are diffused in the ratio 1,274 : 0.508, or 2,507 : 



1. Since the radiant heat transmitted to the reflector by the sun is 



capable of imparting a temperature to the boiler of 520° F. above that 



of the atmosphere, accepting Newton's law that " the temperature is 



as the density of the rays," the temperature imparted to the boiler of 



the sun-motor proves that the temperature of the solar surface cannot 



be less than 520° x 2,507, or 1,303,640° F. (Nature, January, 1884, 



XXIX, 216.) 



Ayrton and Perry have i)resented a paper on the indicator diagram 

 of the gas-engine to the London Physical Society, intended to teach 

 engineers a new mode of studying these diagrams. The paper gives the 

 most recent results obtained with Dowson gas, a large wooden model 

 of the Otto engine enabling the operations during the cycle to be un- 

 derstood. By means of tables of the composition of the Dowson gas 

 and coal gas, of the air required for their combustion, and of their spe- 

 cific heats, as w^ell as those of their products, the characteristic equation 

 of the fluid used in the engine may be determined. Three practical 

 methods of determining the rate of gain of heat by the fluid during the 

 forward stroke are given, this rate being compared everywhere with 

 the rate of doing work, by means of a diagram. If W represent the 

 indicated work in one cycle, 5.64 W is the total energy of combustion 

 of one charge ; and this is expended as follows : 1.45 W is the work 

 done in the forward stroke, 2.22 W is given to the cylinder by radiation 

 in the forward stroke, 1.5 W is carried off through the exhaust-pipe, 

 0.47 W is given to the cylinder as heat after the exhaust- valve opens. 

 {Phil. Mag., July, 1884, V, xviii, 59 ; Nature, May, 1884, xxx, 47.) 



Thurston has published the results of tests made on an Otto gas-en- 

 gine by Brooks and Steward at the Stevens Institute of Technology. The 

 air and gas were both measured by meter, and the fact was proven that 



