388 



1. A number of Mineral and Fossil Organic Specimens, from various 



localities. — Presented by Lord Greenock. 



2. Specimens of Land and Fresh-water Shells, chiefly from the 



neighbourhood of Edinburgh. 



3. Specimens of Marine Shells, chiefly from the Firth of Forth. 



And, 



4. Specimens of Zoophytes, chiefly from the Firth of Forth, — Pre- 



sented by John Stark, Esq. 



John Goodsir, Esq., Conservator of the Museum of the 

 Royal College of Surgeons of Edinburgh, proposed by Pro- 

 fessor Syme, was duly elected an Ordinary Fellow. 



Monday, \^th December 1842. 



The Right Honourable Lord GREENOCK, Vice-President, 



in the Chair. 



The following communications were read : — 

 1. Letter on Terrestrial Magnetism, addressed to the Secre- 

 tary. By Professor Hansteen of Christiania. 



Christiania, the. 22nd April 1812. 

 * * * * I HAVE the pleasure to send you two papers : the first on the 

 changes, which the moment of a magnetical needle or bar undergoes as a 

 function of the elapsed time, and of the variations of the temperature ; the 

 second, in the German language, is an extract of a letter to Professor Kupffer 

 of St Petersburg, exhibiting the changes of the time of 300 horizontal vi- 

 brations, in Christiania, of my invai-iable magnetical cylinder, made by Dol- 

 lond in 1819, from 1820 to 1839. In the Latin Programma, page 17, seven 

 later observations, to this year, are annexed. In the first paper it is demon- 

 strated by experiments, with nine different magnetical cylinders, that the 

 moment M is a function of the time t, elapsed after its being magnetized, of 

 the following form : — 



M= C + Be"''" 

 where = ^1-; is the value of M, when f = eo , f the basis of the natural 

 logarithms, q a constant depending of the quality and hardness of the steel, 

 B = M^ — M gj is the whole variation of M between ? =: 0, and < = « . The 

 moment of every magnetical needle has accordingly a limit C, which it 

 cannot transgress ; and every variable needle may be used to determine 

 the intensity in a voyage, wiien only the three constants, B, C, q, are de- 

 termined by three observations, including the whole time of the voyage. In 

 page 13, you ynl\ find under No. 4, the history of the cylinder belonging to 

 the " Hansteen Apparatus" of the Royal Society of Edinburgh, from No- 

 vember 5. 1821, to October 29. 1826. After its arrival at Edinburgh, it seems 

 to have lost some more of its power, perhaps from coming into a higher 

 temperature. For, according to my calculations, it should already have been 



