198 ANNUAL OF SCIENTIFIC DISCOVERY. 



when surrounded by ice or water, proved the power required to raise one 

 pound of water one degree, and which he valued at the dynamic equivalent 

 of 1,034 Ibs. M. Moya was the first who announced that heat was evolved 

 from agitated water. The second was Mr. Joule, who announced that heat 

 was evolved by water passing through narrow tubes, and by this method 

 each degree of heat required for its evolution a mechanical force of 770 Ibs. 

 Subsequently, in 1845 and 1847 he arrived at a dynamical equivalent of 

 772 Ibs. These experiments had since been confirmed by other philosophers 

 on the Continent. In the present paper, Mr. Rennie stated that his atten- 

 tion was called to the subject by observing the evolution of heat by the sea 

 in a storm, by the heat from water running in sluices. He, therefore, pre- 

 pared an apparatus similar to a patent churn, somewhat similar to that 

 adopted by Mr. Joule, but on a large scale. In the first case, he experi- 

 mented on fifty gallons, or 500 Ibs. of water, inclosed in a cubical box, and 

 driven by a steam engine instead of a weight falling from a given height, as 

 in Mr. Joule's experiment ; secondly, on a smaller scale, by 10 Ibs. of water 

 inclosed in a box. The large machine or churn was driven at a slow veloc- 

 ity of eighty-eight evolutions per minute, and the smaller machine at 

 the rate of 232 evolutions per minute, so that the heat given off by the wa- 

 ter in the large box was only at the rate of three and a half degrees per 

 hour, including the heat lost by radiation ; whereas the heat evolved by the 

 ten gallons of water contained in the small box agitated at 232 evolutions 

 was fifty-six degrees Fahrenheit per hour. Thus the temperature of the 

 water in the large box was raised from sixty degrees to 144 degrees, and 

 the temperature of the water in the small box to boiling point. As an illus- 

 tration, an egg was boiled hard in six minutes. The mechanical equivalent, 

 in the first case, was found to approximate nearly to that of Mr. Joule, but 

 in the latter case it was considerably above his equivalent, arising, very 

 probably, from the difficulty of measuring accurately the retarding forces. 



PRELIMINARY RESEARCHES OX THE ALLEGED INFLUENCE OF 

 ' SOLAR LIGHT ON THE PROCESS OF COMBUSTION. 



The following is an abstract of a paper read before the American Associ- 

 ation for the promotion of Science, on the above subject, by Prof. J. L. Conte. 



A popular opinion has long prevailed in England, and perhaps in other 

 countries, that the admission of the light of the sun to an ordinary fire tends 

 to retard the process of combustion. In some instances, the practice of 

 placing screens before the fireplace, or of closing the shutters of the apart- 

 ment, may be traced to the prevalent belief, that the access of sunlight to 

 the burning materials is unfavorable to the continuance of the phenomenon 

 of combustion. Most physical philosophers very naturally regard this opin- 

 ion as a mere popular prejudice ; probably originating in the well-known ap- 

 parent dulling or obscuration of flames and of solid bodies in a state of ig- 

 nition, which takes place when they are exposed to strong light. The 

 flame of a jet of burning hydrogen is scarcely visible in the diffused light of 

 a clear day ; that of an ordinary alcohol lamp is barely appreciable to the 



