Royal Society. 361 



were blown down raising two or three tons of clay soil with the roots . 

 Several trees thus thrown down fell with their tojis to the W.N. W. 



The writer concludes from these and other observations, that the 

 first and squally part of the storm began from the E.S.E., and blew 

 from S. by W. at about midnight ; and that most injury was done 

 to the slating and roof when the wind was not far from the south. It 

 then gradually veered to the west, till noon, and reached the N.W. 

 point by eight o'clock in the evening of the same day. 



Feb. 21. — A j^aper was read, entitled, " An Account of the Pro- 

 cesses employed in Photogenic Drawing," in a letter to S. Hunter 

 Christie, Esq.. Sec. R.S. By H. Fox Talbot, Esq., F.R.S.* 



A paper was also read, entitled, " A Description of a Hydro- 

 pneumatic Baroscope." By J. T. Cooper, Esq., Lecturer on Che- 

 mistry. 



The liability of the ordinary mercurial barometer to derangement 

 and to fracture, led the author to the construction of an instrument 

 for measuring atmospheric pressure that should be exempt from 

 these objections. It consists of a float, formed by a brass tube, 

 having the shape of the frustum of an inverted cone, nine inches 

 long, two inches in diameter above, and one inch below, and its 

 content being about fourteen cubic inches. From the centre of the 

 upper and wider end, which is closed, a brass wire proceeds, sur- 

 mounted by a cup, for the jjurpose of holding such weights as are 

 necessary for bringing the float, when immersed in water, to the 

 same constant level. The lower and smaller end of the tube is 

 closed by a brass plug, sufficiently heavy to sink the instrument to the 

 proper depth, and maintain its position, and having a small perfora- 

 tion in its centre. This float is inclosed in a case, containing the 

 water in which it is to be immersed, and which is to be raised to a 

 constant given temperature by a spirit lamp burning beneath it. 

 The float being first filled with water, a given portion of this water 

 is poured out into a measure of known capacity, and is consequently 

 replaced by an equal volume of air, the dilatations or contractions of 

 which will, when the temperature is constant, be dependent only on 

 the external pressure of the atmosphere ; and the latter will, there- 

 fore, be indicated by the weights requisite to be placed in the cup of 

 the float, in order to maintain it at the same level in the fluid, on the 

 principle of the hydrometer. The author gives a minute description 

 of all the parts of the apparatus, of the method of using it, and of 

 the adjustments and calculations required for determining by its 

 means the difference of level of two stations. 



Mr. Darwin's paper, entitled, " On the Parallel Roads of Glen 

 Roy, and other parts of Lochaber, &c.," was resumed, but not con- 

 cluded. 



Feb. 28. — The reading of a paper, entitled, " Observations on the 

 Parallel Roads of Glen Roy, and of other parts of Lochaber, with an 

 attempt to prove that they arc of Marine Origin." Jiy Ciiarlcs Dar- 



* This paper was given cnliro in our Number for March ; i)rcs. vol. p. 

 209.— EuiT. 



