92 



REPORT — 1842. 



llesults in the preceding table and the previous reports, showing the progres- 

 sive and increased ratio of deflections, from the 23rd of June 1838 to 

 April 29th, 1842. 



Weight on bar 448 lbs. 



In these experiments the same anomaly is present as in Table I., namely, a 

 decrease of -008 in the deflections, which may be accounted for in the same 

 way as before. These discrepancies are the more apparent, as the deflection 

 in March 1838 was 1*439, in June of the same year it increased to 1*457, 

 and in the February following it returned to 1*433 ; thus corresponding in 

 some degree with the temperature of the room, which varied as the respect- 

 ive numbers 51°, 78° and 54°. In every other respect the bars have been 

 tending to rupture, and since the deflections were taken one of them has 

 broken. 



Viewing the subject in all its bearings, it appears evident from these ex- 

 periments, that time is an element which in a greater or less degree affects 

 the security of materials when subjected to severe and long-continued press- 

 ure. It may at first sight appear that the cohesive powers and the resist- 

 ance may be so nicely balanced as to neutralise each other, and in this state 

 continue ad infinitum, provided there be no disturbing force to produce de- 

 rangement of the parts, and thus destroy the equilibrium of the opposing 

 forces. This cannot, however, be expected : in practice, disturbing causes 

 often occur, and I think Ave may reasonably conclude that long-continued 

 strain will tend to lessen the cohesive force which unites the particles of mat- 

 ter together, and will ultimately destroy that power of resistance which has 

 for the last five years been so strongly exemplified in the above and previ- 

 ously printed experiments. 



Report of the Committee appointed at the Meeting of the British 

 Association held at Plymouth, in 1841, for registering Shocks of 

 Earthquakes in Great Britain. By David Milne, Esq., M.A., 

 F.R.S.E. 



I. The Committee have continued to promote the object for which they were 

 appointed, by sending additional instruments to Perthshire, where shocks of 

 earthquake still continue to be felt. The following is a list of the shocks ob- 

 served at Comrie since the date of the report given in last year to the Asso- 

 ciation. 



In the following Table column 1 represents the day of the month, column 

 2 represents the total number of shocks felt during that day, column 3 re- 



