271 



In another experiment a heavier needle was suspended by a fine 

 wire, and when heated by exposure to the sun its decrease of inten- 

 sity was ascertained by torsion of the wire, and was found to cor- 

 respond nearly with the author's previous determinations ; but the 

 terminal arc, after fifty vibrations made in the sun, was found 

 always considerably less than after the same number in the shade, 

 the initial arcs being the same in both cases. Other observations 

 made in strong sunshine, and of which a detail is given, led to the 

 same conclusions ; the terminal arc in the shade, after forty vibra- 

 tions, being 14, and in the sun only 8^, the initial arc being 90. 



That this effect does not arise from change of temperature and 

 intensity in the needle is evident from the observations themselves. 

 To show that it does not arise from change of temperature in the 

 brass box, the author heated the box over a fire till its heat was 

 barely supportable by the hand ; and the needle being vibrated al- 

 ternately in the box so heated, and in the cold box (but in neither 

 case exposed to the sun), the effect of increased temperature was 

 found decidedly and considerably the reverse of that of the solar ra- 

 diation, the terminal arc being materially increased by the heat, a 

 circumstance, he thinks, indicative of a diminished capacity for 

 magnetism in brass at an elevated temperature. 



The author next tried the effect of an elevation of temperature in 

 the needle itself, by dipping it in boiling water, but found no sen- 

 sible effect on the terminal arc. 



The small accelerations in the times of vibrations in the experi- 

 ments first described, the author attributes to the diminution of the 

 arcs. The first observations in which the peculiar effect was noticed 

 were made June 4, 1824; and he regrets that his absence from home 

 during the hot and clear weather of the summer of 1825, prevented 

 his extending the inquiry by further and obvious experiments. 

 Meanwhile he regards these observations as tending considerably to 

 remove the doubts raised respecting the influence of the violet ray 

 in Professor Morichini's experiments, arising from their repeated 

 failures in the ablest hands. 



On the mutual Action of Sulphuric Acid and Alcohol, with Observa- 

 tions on the Composition and Properties of the resulting Compound. 

 By Mr. Henry Hennell, Chemical Operator at Apothecaries' Hall. 

 Communicated by W. T. Brande, Esq. Sec. R.S. Read March 9, 

 1826. [Phil. Trans. 1826, Part III. p. 240.] 



At the commencement of this paper Mr. Hennell describes certain 

 peculiarities in the properties of oil of wine, which induced him to 

 consider sulphuric acid as one of its proximate 'elements ; and on 

 following up his analytical experiments upon it he found that about 

 37 per cent, of that acid might be obtained during its decomposition, 

 although in its original state it affords no indications of that acid by 

 the tests of the soluble salts of baryta, a circumstance which he re- 

 fers to the presence of hydrocarbon exerting a peculiar saturating 



