Intelligence and Miscellaneous Articles. 381 



a process of his own is the same as one of mine, though it is 

 not ; he says that I sometimes suppose the free time to be 

 constant, and sometimes to depend on the number of atoms, 

 when I do not ; and, lastly, that I have not stated what 

 meaning I attach to t, when on page 238, line 44, I have 

 defined it to be the free time multiplied by the number of atoms. 

 I am, Gentlemen, 



Your obedient servant, 

 Trinity College, Cambridge, J. J. THOMSON. 



Feb. 14, 1887. 



XL IV. Intelligence and Miscellaneous Articles. 



ON CEKTAIN MODIFICATIONS OF A FORM OF SPHEEICAL 



INTEGRATOR. 

 To the Editors of the Philosophical Magazine and Journal. 



GrENTLEHEN, 



T HAD occasion recently to read in the Philosophical Magazine 

 -*- (August 1886) the very interesting description of a " Spherical 

 Integrator," designed by Mr. Frederick John Smith, and which 

 appears to be a modification of that of Prof. Hele Shaw. But the 

 first conception of these apparatus, and it is to this that I wish to 

 call your attention, belongs without doubt to me, as in No. 630 of 

 1 Nature'' (Nov. 24, 1881) I gave a description of an "Anemometer 

 Integrator" founded on the same principle, and which was after- 

 wards mentioned in the Quarterly Journal of the Royal Meteoro- 

 logical Society, No. 43(1882), by Mr Laughton ("Historical Sketch 

 of Anemometry and Anemometers "). 



The modification designed by Mr. P. J. Smith tending to do 

 away with or lessen, as much as possible, the moment of inertia of 

 the sphere, appears to me excellent, especially if it is to transmit 

 velocities of small magnitude. But when it is simply required to 

 register that of the wind upon a moderate scale, I believe that the 

 primitive form suffices ; and after several trials which I have made, 

 an ivor} r ball rolling on bronze cylinders is that which gives the best 

 results. 



I beg, Gentlemen, that you will allow this claim of priority to 

 appear in your valuable Journal, and also that you will accept my 

 most sincere thanks and the assurance of my marked regard. 



Madrid Observatory, March 12, 1887. V. Ventosa. 



ON THE STRENGTH OF THE TERRESTRIAL MAGNETIC FIELD 

 IN BUILDINGS. BY M. AIME W1TZ. 



In consequence of the removal of my laboratory to a new 

 building in which the joists and framework are of iron, I have 

 been led to determine exactly the values of the horizontal com- 

 ponent in the various rooms used for Physics, with a view to 

 certain researches which I have undertaken. I have observed 



