TRANSACTIONS OF THE SECTIONS. 7 



ployed the results obtained at forty stations distributed over the whole, and he 

 arranged these for a final conclusion in groups and lines related to the great natural 

 features of the county. By the method of least squares it was found that the Isoclinal 

 lines made with the meridian, on the average of the whole county, angles of 70° 31' 

 to the east of north ; that the rate of maximum augmentation of dip was, on a line 

 at right angles to this, 'SSS parts of a minute of dip for one geographical mile. But 

 on examining by the same method, or by a simple graphical process, the direction of 

 these lines in diflferent parts of the county, it was found that they were bent into 

 large curves, so as to^retire southward across the great vale of York-, and to advance 

 northward on the hilly regions to the west and east of this vale, but especially turn- 

 ing up northward in the country between Flamborough Head and the mouth of the 

 Tees. 



Besides other ways of viewing these phsenomena, the author called attention to 

 the probable effect of the inclination of the strata, which by varying the direction of 

 maximum pressure, as in the case of anticlinals and synclinals, would necessarily 

 affect by a similar variation the direction of the suspended needle ; and he proposed 

 as a new and curious question, the possibility of seeing, by help of the magnetic 

 needle, through the parts of the crust of the earth near the surface, so as to trace the 

 deep-seated axes and centres of movement, which by no other way could be made 

 sensible to the geologist*. 



On Magnetism. By Professor PliJcker, Bonn. 



By repeating Dr. Faraday's experiments on diamagnetism six years ago, I first 

 observed that a piece of charcoal suspended between the two poles of a magnet was 

 either repelled or attracted, according to the distance from the poles. The same day 

 I observed the same phsenomenon, when I substituted a prism of tourmaline for the 

 piece of charcoal ; but these phsenomena, similar as they are in appearance, were 

 produced by quite a different kind of magnetic action. I made a communication to 

 the British Association, when I attended the Swansea meeting, on the particular 

 action of a magnet on crystals, but I did not speak then on the other class of 

 phsenomena, the transition from magnetic attraction into diamagnetic repulsion, 

 which takes place on mixed bodies when the power of the magnet increases. I had 

 deduced from a long series of facts, that by increasing this power the action on dia- 

 magnetic bodies augments more rapidly than the action on magnetic ones. I believe 

 it is a mathematical law, and being such a one, whatever may be its physical 

 interpretation, is out of the reach of attack ; but I had not the satisfaction to see it 

 generally adopted, therefore I undertook last summer a new series of experiments, 

 which will give, I think, to that law a more universal character and a more distinct 

 description. 



The experimental results I immediately obtained may be represented best by curves, 

 giving for the different bodies I examined the law according to which the attraction 

 produced by the electro-magnet varies with the intensity of the current made use of. 

 If the induced magnetism were always in the same ratio as the inducing power, if 

 there were no resistance against further magnetization either in the electro-magnet 

 or in the body examined, that curve must be a parabola ; on the contrary, if the 

 body were saturated with magnetism, it would be a straight line. Now by examining 

 different substances, I got curves passing through all intermediate steps from one 

 limit to the other one. Nickel is nearly saturated when I make use of one single 

 element of Grove ; the hydrate of oxide of cobalt presents, under the same condi- 

 tions, scarcely any resistance against magnetization. The resistance is also very 

 small in oxygen ; it is very small too in bismuth and phosphorus, the two diamag- 

 netic bodies I examined, wherein the repulsion by the magnet is to be substituted 

 for the attraction exerted' on magnetic substances. Then comes oxide of nickel, 

 oxide of iron, iron, cobalt, and at last nickel. 



From the curves I have spoken of, we may deduce others giving the intensity 



* In the discussion which followed, Prof. Pliicker confirmed .the truth of the supposition 

 of Prof. Philhps, that such magnetic effects would follow from the varying direction of maxi- 

 miun pressure, but whether the effects would be sensible must be settled by experiment. 



