xl REPORT — 1864. 



of which two have been before me for several years, and the third has lately 

 come before me with great force. 



1st. You are in some measure aware of the discordances which I have 

 found in observations of the dipping-needle, made Avith the smallest con- 

 ceivable change in the circumstances of bearing, or even (as in some experi- 

 ments which I have lately transmitted to Prof. Stokes) without lifting the 

 needle at all. I am sure the Kew Observatory would do well in thoroughly 

 investigating this matter by experiment. 



2nd. I have been troubled for many years with small displacements in 

 the trace of the vertical-force photograph. I should bo glad to have these 

 investigated at the Kew Observatory ; but it wiU be necessary for this pur- 

 pose to modify the adjustments of the vertical-force instrument at Kew, 

 which at present is incompetent to exhibit such displacements, and masks 

 all that may ever have occurred. 



3rd. I should be very glad indeed to have a set of experiments on the 

 temperature con-ections of the force of a magnet, made by heating it in liot 

 air instead of by hot water. My own experiments leave us in most distress- 

 ing doubts. 



It win give me great pleasm-e to cooperate as far as possible with the Kew 

 Committee in these matters ; any record of our experiments and any ap- 

 paratus that we can possibly spare wiU be at their command. 



I am, my dear Sir, 



Yours very tnily, 

 To J. P. Oassiot, Esq., (Signed) G. B. Aiky. 



CPmirman of the Kew Observatory Committee. 



VI. 



Clapham Common, July 13, 1864. 

 My dear Sir, — I have your letter of the 11th, suggesting certain experi- 

 ments in relation to magnetic instruments, which I Avill lay before the Kew 

 Committee at its next meeting. 



I have in the mean time forwarded your letter to Mr. Stewart, the 

 Director of Kew Observatory, who will, I am confident, give it his best 

 attention. I remain, yours truly, 



(Signed) J. P. Gassiot. 



To O. B. Airy, Esq., Astronomer Boyal. 



VII. 



Kew Observatory, July 30, 18C4. 



Mt dhar Sir, — I have i^erused Mr. Airy's letter, addressed to yourself as 

 Chairman of the Kew Committee, in which he suggests that certain experi- 

 ments should be made at the Kew Observatory, and I now reply to your 

 request that I should report concerning this letter for the information of the 

 Committee. 



From the correspondence which has passed between Mr. Airy and yourself, 

 I have little difficulty in finding the proper basis for this report ; the ques- 

 tion resolves itself into the following: — Is it expedient in the interest of 

 magnetical science that the Committee should undertake these experiments ? 



If the suggestions of Mr. Airy refer to points which have not been settled, 

 the Committee are surely indebted to him for bringing these before them ; 

 but if, on the other hand, it be the opinion of the Committee that these 

 points have already been discussed and finally disposed of, Mr. Airy cannot 

 blame them if they decline making the experiments which he suggests. 



