76 



Messrs. J. H. Gray and J. B. Henderson. [Mar. 2, 



occur in the day and only one in the night. In the former case the 

 negative portions of the component correspond with the reduced 

 morning and afternoon temperatures of the short day, and in the 

 latter the two positive phases correspond with the higher temperature 

 of the mornings and afternoons of the longer day. 



These conclusions are in conformity with those previously in- 

 dicated. 



The available data are insufficient to enable us to say whether 

 the corresponding results connected with the fourth component are 

 as fully supported by observation as in the case of the third, but the 

 facts so far as they go confirm this view. 



It may also be pointed out that, if instead of reckoning the epochs 

 of maximum from midnight, that nearest to noon had been adopted, 

 it would have been seen that there is a distinct tendency for all these 

 epochs to approach noon, affording evidence, which is perhaps hardly 

 required, that they are all closely dependent on the passage of the sun 

 over the meridian. 



For Greenwich the results would be — 



Winter. Equinox. Summer. 



1st component 222° 215° 210° 



2nd „ 200 198 181 



3rd „ 194 (193) 



4th „ 190 (193) 196 



In the case of the third and fourth components, the figures enclosed 

 in brackets are epochs of minimum. 



II. " The Effects of Mechanical Stress on the Electrical Resist- 

 ance of Metals." By James H. Gray, M.A., B.Sc, and 

 James B. Henderson, B.Sc, International Exhibition 

 Scholars, Glasgow University. Communicated by Lord 

 Kelvin, P.R.S. Received February 10, 1893. 



(Abstract.) 



This investigation was begun for the purpose of obtaining an 

 easily worked method of testing the effect of any mechanical treat- 

 ment on the density and specific resistance of metals. 



For alteration of density, copper, lead, and manganese copper 

 wires were tested. The effect of stretching was always to diminish 

 the density, the alteration being small however : for copper about 

 \ per cent., and for lead -| per cent. The effect of drawing through 

 holes in a steel plate was somewhat greater, showing at first an in- 



