09 



application of the magnetical influence in engineering, in tunneling, 

 and in mining, for determining the thickness of solid masses in dif- 

 ferent situations where circumstances preclude the possibility of 

 direct measurement. He adduces a variety of instances in which 

 the information thus obtained would prove of the greatest value, in 

 directing the operations in progress, or determining those to be un- 

 dertaken, and frequently in preventing the occurrence of accidents 

 which the want of such knowledge may occasion. He concludes 

 with a statement and explanation of various practical directions for 

 the employment of the method recommended. 



A paper was read, " On a new Register Pyrometer for measuring 

 the Expansion of Solids." Part II. By J. F. Daniel], Esq. F.R.S., 

 Professor of Chemistry in King's College, London. 



In this paper, which is a sequel to that published in the Philoso- 

 phical Transactions for 1830, the author prosecutes the series of 

 experiments he had commenced on the dilatation of the metals : 

 pursuing the comparison between the results of the experiments of 

 Dulong and Petit, with those given by his own instrument. He 

 finds a striking accordance between them in the case of copper, as 

 he had already done with respect to iron and platina. He gives the 

 result of some trials which he made with a view to obtain registers 

 of uniform composition, so as to preclude the necesshy of deter- 

 mining the rate of expansion in each individual instance. The re- 

 sults of his experiments on the dilatation of the metals are given in 

 tables- the first showing in arcs of the scales the expansions of four 

 metals from 62° to 212°, and thence to 662° of Fahrenheit; and 

 their respective melting points : and the second, exhibiting the ex- 

 pansion of certain alloys to the same points. The experiments on 

 the melting point of cast iron give a mean of 2768°, and present a 

 remarkable coincidence with the corrected temperature deduced 

 from the expansion of a platina bar, plunged into melted cast iron, 

 which was 2786° ; thus affording a conclusive proof of the accuracy 

 of the pyrometer, and of its competency to determine fixed and 

 comparable points of very high temperature. The author accord- 

 ingly thinks himself warranted in recommending the introduction 

 of the instrument extensively in all arts and manufactures, where it 

 is an object to regulate high temperatures, and where it is calcu- 

 lated to determine many questions of the highest importance both 

 to practical and theoretical science. 



Two papers were read; the one entitled, et On the Influence of 

 Screens in arresting the Progress of Magnetic Action :" the other, 

 " On the Power of Masses of Iron to control the attractive Force of 

 a Magnet." By William Snow Harris, Esq. F.R.S. 



The object of the first paper is to show that every substance 

 susceptible of magnetism by induction, when interposed as a screen, 

 tends to arrest the action of a magnet upon a third substance: this 

 intercepting power being directly as the mass, and inversely as the 

 susceptibility to induced magnetism. Thus, although a single plate 



