368 Mr. Thomas Gray on a New 



unsatisfactory and unreal, too much attention having been 

 given to purely literary points, to the almost entire exclusion 

 of the realities connected with the phenomena of dew, and the 

 interpretation to be put on them. No one, I am sure, regrets 

 the unfortunate direction the discussion has taken more than 

 I do. It could not, however, be avoided, owing to the direc- 

 tion from which the attack was delivered. 



After all this difference of opinion it is a comfort to find 

 one point on which we are agreed, namely " not to write again 

 on this subject \" and in closing the discussion I wish to 

 thank Mr. Tomlinson for his criticisms, because I am sure his 

 objections will be the objections of many others to my conclu- 

 sions ; and though I fear I have not succeeded in making a 

 convert of him, I may perhaps have been more successful 

 with those whose ideas are not so defined and stereotyped by 

 frequent writing on the subject. I think, however, I can 

 assure Mr. Tomlinson that when he candidly and calmly con- 

 siders the result of my investigations, he will not find them so 

 heterodox as he at present seems to think ; nor do I think 

 that my observations will entirely " supersede the labours of 

 previous observers " for whose work he has so much respect, 

 though some of their views Avill require modification to meet 

 the present state of our knowledge. 



Yours truly, 

 Darroch, Falkirk, JOHN AlTKEN. 



September 11, 1886. 



XLV. On a new Standard Sine- Galvanometer. 

 By Thomas Geay, B.Sc, F.R.S.E.* 



''PHE standard galvanometers commonly employed for the 

 determination of currents in absolute measure consist 

 either of one bobbin of large radius, having a groove of rela- 

 tively small breadth and depth filled with wire, or of two 

 such bobbins mounted with their planes parallel and at a 

 distance apart equal to the radius of either coil. These coils 

 are suitably mounted for use either as sine- or as tangent- 

 galvanometers. The object of making the coils of large 

 radius is twofold — first, in order that it may be possible to 

 measure it with sufficient accuracy, and second, in order that 

 the magnetic field, produced by the current, may be of nearly 

 uniform strength near the centre of the coil. So far as uni- 

 formity of field is concerned, the double coil, or Helmholtz 

 arrangement, is all that can be desired ; but it introduces a 

 multiplicity of measurements, one at least of which, namely 



* Communicated bv the Author. 



