196 Proceedings of the Royal Society of' Edinburgh. 



4. Notice of further Discoveries at Burdiehouse. By Dr 

 Hibbert. 



The author announced that, since his former paper was read, on 

 the organic remains of the limestone quarry at Burdiehouse, disco- 

 veries of still greater interest had been made. These chiefly con- 

 sist of the remains probably of a large animal of the Saurian tribe, 

 namely, what appears to be the epiphysis of one of the vertebrae, 

 presenting, when broken across, the cancellated structure of bone — 

 several large scales obtained by Mr Connell, — and, in particular, a 

 large and beautifully perfect tooth, two inches and a quarter long, and 

 covered with its enamel, which is quite entire. The remains here 

 alluded to were exhibited and presented by the author and Mr Con- 

 nell to the Society's Museum. 



1834, Jan. 6. — Sir T. M. Brisbane in the Chair. The 

 following Communications were read. 



1. On the Investigation of Magnetic Intensity, by the Oscilla- 

 tions of a Horizontal Needle. By William Snow Harris, 

 F. R. S. 



The chief disturbing causes by which the magnetic intensity, as 

 ascertained by the oscillations of the horizontal needle, are affected, are 

 !• Variations in the air in which they are performed ; 2. The influ- 

 ence of changes in the mechanical conditions incidental to the mode 

 of suspending the needle ; 3 Changes in the disposition and intensity 

 of the magnetism of the needle from heat and other causes- 



These causes of disturbance the author proceeded to investigate. 



I. He compared the oscillations of the needle vibrating in air, with 

 those of the same needle oscillating ifi vacuo ; and he minutely de- 

 scribed the apparatus which he had contrived for allowing the needle 

 to vibrate freely in an exhausted receiver, and his mode of deter- 

 mining the arcs of vibration. This apparatus enabled him to ap- 

 preciate the resistance of air to the oscillations of the needle, and its 

 effect in rendering unequal the duration of vibrations performed in 

 long and in short arcs. Hence he inferred the impossibility of ascer- 

 taining the alleged diurnal changes of magnetic intensity by the com-; 

 mon apparatus. 



II. The second source of disturbance he endeavoured to obviate by 

 a more accurate mode of suspending the needle ; by which its centre 

 of gravity and point of magnetic neutrality should be made to coin- 

 cide. This tlie author proposes to accomplish by greater care in find- 

 ing its true centre, and in adjusting its horizontality by means of 

 small sliding counterpoises of platinum on each arm. 



HI. The influence of increase of temperature on the magnetic 

 needle has generally been considered as lowering the tension of its mag- 

 netism ; and it has been represented as again restored by cold : 

 but the author's experiments seemed to prove the contrary, when the 



