422 Prof. Tyndall on Reciprocal Molecular Induction. 



gatiou, twenty-four detailed rock analyses have been already 

 completed." In a return to au order of the House of Commons 

 on a motion made by Mr. George Alexander Hamilton, bearing 

 date 3rd May, ISoi, I tiud the following statement: — "Con- 

 siderable progress has been made with a very extended investi- 

 gation into the composition of the felspathic and hornblendic 

 rocks of the county Wicklow ; the analytical portions of this 

 work, perhaps the most laborious and extensive of its kind ever 

 undertaken, will include between 400 and 500 quantitative ana- 

 lyses of rock specimens." In the Report to the Board of Trade, 

 16th January of the present year, it is again represented that 

 " in the chemical department of the museum the examination of 

 the felspathic rocks, &c. has made considerable progress." 



When we consider that this investigation was undertaken by 

 Sir Robert Kane in a public capacity, and in conjunction with 

 the officers of the Geological Survey, it must be allowed that the 

 public have a right to ask for information on the subject ; and 

 when we consider that Sir Robert Kane publicly pledged himself 

 to produce his analyses, we must conclude that he is bound as a 

 man of science to redeem his pledge and substantiate his statement. 

 I remain, Gentlemen, 



Your obedient Servant, 



Trinity College, Dublin, Joseph A. GalbrAITH. 



November 14, 1855. 



LIX. On Reciprocal Molecular Induction. 

 To Prof. W. Thomson, F.R.S. 

 My DEAR Sir Royal Institution, Nov. 26, 1855. 



THE communication from Professor Weber which appears in 

 the present Number of the Philosophical Magazine, has re- 

 minded me, almost too late, of your own interesting fetter on 

 the same subject published in the Api'il Number of this Journal. 

 A desire to finish all I have to say upon this question at present 

 induces me to make the following remarks, which, had it not 

 been for the circumstance just alluded to, might have been inde- 

 finitely deferred. 



With reference to the mutual action of a row of bismuth particles, 

 you say that "it is perfectly easy to demonstrate that it must be such 

 as to impair the ' diamagnetization ' when the line of the row is 

 parallel to the lines of force" (the 'must,' you will remember, 

 is put in italics by yourself). From this you infer, that in a 

 uniform field of force a bar of bismuth would set its length 

 along the lines of force. Further on it is stated that this 

 action is " demonstrated with as much certainty as the paral- 

 lelogram offerees;" and you conclude your letter by observing 



