292 DR. J. p. JOULE ON THE FREEZING-POINT. 



cordingly^ soon after I had a small and more portable in- 

 strument constructed for this special purpose ; but up to 

 this time I had not given it any sufficient trial. On the 

 occasion of a recent visit. Dr. Joule assisted at some ex- 

 periments with this instrument. The results have con- 

 vinced us both that it will be quite practicable to improve 

 it so that it may serve for a determination of the dip within 

 a minute of angle. I hope, accordingly, before long to be 

 able to communicate some decisive results to the Society, 

 and to describe a convenient instrument which may be prac- 

 tically usefal for the observation of this element. 



XXV. Observations on the Alteration of the Freezing-point 

 in Thermometers, By Dr. J. P. Joule, F.E.S., V.P. 



Read April i6th, 1867. 



Having had in my possession, and in frequent use, for 

 nearly a quarter of a century, two thermometers, of which 

 I have from time to time taken the freezing-points, I think 

 the results may offer some interest to the Society. Both 

 thermometers are graduated on the stem, and are, I believe, 

 the first in this country which were accurately cahbrated. 

 Thirteen divisions of one of them correspond to one degree 

 Fahrenheit. It was made by Mr. Dancer, in the winter 

 of 1843-44. My first observation of its freezing-point was 

 made in April 1 844. Calling this zero, my successive ob- 

 servations have given 







April 1844. 



8-8 



February 1853. 



5-5 



February 1846. 



9-5 



April 1856. 



6-6 



January 1848. 



III 



December i860. 



6-9 



April 1848. 



11-8 



March 1867. 



The total rise has been, therefore, -gi of a degree Fahren- 



