TRANSACTIONS OF THE SECTIONS. 



245 



On a Mode for Suspending, Disconnecting, and Hoisting Boats attached to 

 Sailing Ships and Steamers at Sea. By E. A. Wood. 



APPENDIX. 



Mathematics and Physics. 



On a remarkable specimen of Chalcedony, belonging to Miss Campbell, and 

 exhibiting a perfectly distinct and well-drawn landscape. By Sir David 

 Brewster, K.H., LL.D., JF.R.S. 



Sir David Brewster, who had examined the specimen, ascertained that the land- 

 scape was not between two plates subsequently united, but was in the interior of a 

 solid piece of chalcedony. 



He stated that chalcedony was porous, and that the landscape was drawn by a 

 solution of nitrate of silver, which entered the pores of the mineral. 



Sir David Brewster stated that above thirty years ago he had examined a simdar 

 specimen, belonging to the late Mr. Gilbert Innes of Stow, who had paid a large 

 price for it. Having no doubt that the figure of a cock which it contained was drawn 

 by nitrate of silver, introduced into the pores of the mineral, he induced the late 

 Mr. Somerville, a lapidary in Edinburgh, to make the experiment ; and he succeeded 

 in introducing the figure of a dog into the interior of the mineral. 



The curious fact, however, displayed by the specimen now exhibited to the Section, 

 is that the landscape had entirely disappeared after being kept four years in the dark. 



When the specimen was received yesterday from Miss Campbell, the landscape was 

 wholly obliterated ; but after the exposure of an hour this morning, it reappeared 

 in the distinctest manner, as may be seen by looking at it against a white ground. 



It is of importance to remark that the figure of the cock in Mr. Innes's specimen 

 which was very strong in its tint, had never been seen either to disappear or to 

 diminish in its tints. 



On the Connexion between the Solar Spots and Magnetic Disturbances. 

 By Sir David Brewster, K.H., LL.D., F.B.S. 



On a Method of reducing Observations of Underground Temperatures. By 

 J. D. Everett, Professor of Mathematics in Kings College, Windsor, 

 Nova Scotia. 



The paper commenced by an acknowledgment of obligation to Prof. W. Thomson, 

 LL.D., of Glasgow, for a knowledge of the principle on which the method is based. 

 The objects sought to be attained are, — 1st, to express the temperature in terms of 

 the time of year (on the average of a number of years) ; and 2nd, to deduce the 

 conducting power of the soil. The paper contained an application of the method to 

 temperatures observed during the seventeen years IS38-54, at the Royal Edinburgh 

 Observatory. The underground thermometers at this Observatory are four in number, 

 and are at depths of 3, G, 12 and 24 French feet respectively. Their average tem- 

 peratures for each calendar month were — 



