538 Proceed ings . 



Genekal Meeting. 

 C. Hulke, F.C.S., President, in the chair. 



Paper-^. — 1. " On Terrestrial Magnetism," by the Hon. 

 Eobert Hart, M.L.C. (Transactions, p. 129.) 



The Hon. R. Pharazyn said that on hearing the paper read he had 

 heen impressed hy the fact that it contained several ingenious theories 

 which w(juld require a great deal of careful examination before they could 

 be accepted as sound. Mr. Hart's statement that " the earth in its 

 diurnal revolution cuts the lines of physical force which hold the earth 

 in its place," seemed a very metaphysical one. What are " the lines of 

 physical force," and how could cutting them produce friction? Then, 

 again, what evidence had we tliat the increase of sun-spots increased the 

 force of gravity ? 



The Hon. R. Hart explained that what he meant was that sun-spots 

 were caused by the removal of the cloudy envelope of the sun's photo- 

 sphere, which thus permitted the action of gravity to be more intense. 

 It was like the removal of a blanket from before a source of heat. 



The Hon. R. Pharazyn. — Precisely ; but that is what I deny to be 

 possible. Gravity is a force which acts according to what is commonly 

 stated as the law of inverse squares and direct mass. Now, there is not 

 the slightest reason to suppose that this force can be affected, as light 

 and heat may be, by any screen placed between the attracting bodies. 

 Were this the case it would be an easy subject for mathematical calcula- 

 tion, and, considering the immense amount of attention that has been 

 directed to the theory of gravitation, I do nob see how it could have 

 escaped notice. Then, too, if what causes sun-spots "intensifies the 

 action of the sun's gravity," its effect would bo apparent in astronomical 

 observations and in the mathematical deductions based upon them. 

 Nothing of tlie kind is ever heard of, however. I fancy Mr. Hart has 

 confused certain nragnetic forces with those of gravitation. Under certain 

 conditions magnetic lines of force may be developed which, when cut by 

 a moving body, offer what I thnak Professor Huxley has described as a sort 

 of " sticky resistance," like the resistance caused by an imperfect fluid. 

 There is, however, nothing analogous to this in gravitation. There are 

 several other points in ^fr. Hart's paper which I might touch upon, but 

 I will not take up the time of the meeting any further. On the whole 

 I am mclined to think, " as at present advised," that, ingenious and sug- 

 gestive as j\Ir. Hart's paper is, a careful examination of it would show 

 that the theories advanced in it are not ni accordance with physical 

 facts. 



Sir J. Hector, although he must differ from the author, was pleased 

 to hear a paper on this subject, especially as it brought up the question 

 of magnetic observations. Nothing had been done in the matter since 

 the first surveys. He believed the same instruments could be obtained 

 again for use, so that the magnetic survey could be brought up to the 

 present date. It would be a most important adjunct to the Geological 

 Survey in detecting deep-seated lodes and faults, &c. 



I\Ir. Trcgear did not think dry air could produce sufficient friction 

 to account for Llr. Hart's theory. 



Mr. Travers said the magnitude of the sun must be taken into con- 

 sideration in relation to its distance, and it was not surprising that it should 

 exercise magnetic effects on our globe. There were many cases of intense 

 electrical disturbances. 



The' President said it was difficult to give an opinion without studying 

 the paper. Sun-spots did affect the earth as magnetical disturbances. 

 There was a connection, but beyond that he was not prepared to go at 

 present. 



