Rev. S. J. Perry on the Magnetic 



[J and 17 y 



The broken thermometer was the earliest constructed upon the plan now 

 proposed, and it was consequently not quite so well finished as subsequent 

 practice has secured for those of later construction. The results of the 

 trial under the higher pressures showed an increase in the amount of com- 

 pression experienced by the unprotected instruments rising in one instance to 

 as much as 1 1 0, 5 F. With the protected instruments the rise did not exceed 

 1°'5, due, as before, to the heat evolved from the water by its compression. 



A pressure of 3 tons, it may be observed, would be equal to that of 448 

 atmospheres of 15 lb. upon the square inch ; and if it be assumed that the 

 diminution in bulk of water under compression continues uniformly at the 

 rate of 4/ millionths of its bulk for each additional atmosphere, the reduc- 

 tion in bulk of water under a pressure of 3 tons upon the square inch will 

 amount to about of its original volume. This probably is too high an 

 estimate, as the rate of diminution would most likely decrease as the 

 pressure increases. 



IV. " Magnetic Survey of the West of France." By the Rev. Stephen 

 J. Perry, F.R.A.S., F.M.S. Communicated by the President. 

 Received June 3, 1869. 



(Abstract.) 



This survey was undertaken by the Rev. W„ Sidgreaves and myself in 

 connexion with the Observatory at Stonyhurst College. The instruments 

 employed were those in constant use for the monthly observations of the 

 magnetic elements at this observatory, i. e. Barrow's dip-circle, No. 33, a 

 unifilar by Jones, and Frodsham's chronometer, No. 3148. A portable 

 altazimuth and an aneroid barometer were kindly placed at our disposal by 

 the late Mr. Cooke. 



A complete set of observations of the dip, declination, and horizontal 

 intensity were taken at the following stations : — Paris, Laval, Brest, Vannes, 

 Angers, Poitiers, Bordeaux, Abbadia (near Hendaye), Loyola, Bayonne, 

 Pau, Toulouse, Perigueux, Bourges, Paris (a second time), and Amiens. 

 The chronometer was compared on every possible occasion, and its rate was 

 found to be nearly always 2 s per day. 



The dip was observed according to the description of the observation given 

 by the President of the Royal Society in the * Manual of Scientific Inquiry.' 



The method of vibrations and deflections was invariably adopted for 

 determining the horizontal component of the intensity. For the declination 

 it was deemed most convenient to find the azimuth of a fixed mark by 

 observing transits of the sun with Cooke's altazimuth, and then to measure 

 the azimuthal angle between the magnet and the fixed mark with Jones's 

 unifilar. Dr. Lloyd's method, by reflection, was made, use of only at Brest. 

 The results of these observations, reduced to the epoch January 1st, 18G9, 

 are contained in the following Table :— * 



