230 Royal Society .— - 



or two of the instrument will join the separated columns and put all 

 right. 



The instrument is thus constructed : — The vertical tube, including 

 the bulb, is first made and filled with mercury to the proper height, 

 and the magnetic index is introduced ; then the horizontal tube is 

 joined, and the spirits of wine and the horizontal index are introduced. 

 The bulb is then placed in a freezing mixture, in order that the 

 mercury may retreat as far as possible, followed by the spirits 

 of wine. The tube is then sealed, care being taken that the bore 

 shall end in a small rounded chamber; for if pointed, some of the 

 spirits would be apt to lodge there, whence it would be difficult to 

 remove it. The object of cooling the bulb before sealing off, is that 

 we may have as much air in the tube as possible ; for its pressure, as 

 already mentioned, enables the spirits to follow the mercury when 

 the latter falls. 



To graduate the instrument, set it with the mercurial stem hori- 

 zontal in melting ice, then point off the extremity of the mercurial, 

 and also of the spirit column as corresponding to 32° Fahr. Perform 

 a similar operation in water at 42°, 52°, 62°, &c.,and also in freezing 

 mixtures down to zero, or lower if necessary. 



In conclusion, if used as a wet-bulb thermometer, this instrument 

 will give us the maximum and minimum temperatures of evaporation 

 obtained under precisely the same circumstances. 



" On the Expansion of Metals and Alloys." By F. Crace-Calvert, 

 Esq., F.R.S., and G. Cliff Lowe, Esq. # 



One of us having been engaged for some time in investigating 

 several of the properties of pure metals, it was thought desirable to 

 take advantage of having pure metals at our disposal, together with 

 a series of definite alloys of those metals, to determine their rate of 

 expansion. And we were encouraged in pursuing this course of 

 investigation, by finding that several of the authors who had pre- 

 viously published tables of the expansion of metals differed widely 

 in their results. These discrepancies, having reference to some of 

 the metals most extensively used, might, we thought, be due either 

 to the method employed, or to the fact that metals of different de- 

 grees of purity had been experimented upon. Therefore, being sure 

 of the purity of the metals that we intended to employ, we had 

 recourse to a method the accuracy of which we trust will appear 

 satisfactory. 



Owing to the difficulty of obtaining the metals in a pure state in 

 large quantities, we found it necessary to employ square bars, having 

 a length of 60 millimetres by 10 millimetres of diameter. We 

 therefore devised a process to determine with accuracy the expansion 

 of such short bars. This, we believe, we have effected, as our appa- 

 ratus will easily indicate an expansion amounting to the 50,000th of 

 an inch, or about the 2000th part of a millimetre. 



Omitting the description of our apparatus and of the details of 

 our operations, which would be long for this abstract of our results, 

 we give here a Table of the general results obtained with the fol- 

 lowing metals : — 



