Characterisation, especially by Letters 467 



even sea-sick-making power of the sea. Now what element or elements should be measured in 

 order to show this? Am I right in supposing that the two measurements of maximum height 



i 





during the past (say) 5 minutes and the sum of the heights during the same or some other 

 uniform period would give this? The first, alone, would distinguish between big waves and little 

 waves, tht! last would make the further distinction between an abrupt tumultuous sea and 

 simple regular waves. Do not trouble about the mechanics part as yet. These and many 

 other elements can easily (I think) be measured and I can readily explain and show drawings. 

 NV liat I merely want to know is ivhat would (for the purposes of those who read our weather 

 reports and of ship insurers who dispute claims for wrecks on our coasts, on the ground that 

 the weather was not really bad, and who apply to our office for evidence) be the best elements 

 to measure. 



Pray look at the July number of the Philosophical Magazine, at a paper by George Darwin 

 on interpolation. It may greatly improve our office calculating. I had begged him to examine 

 and investigate the subject, especially with a view of interpolating in three dimensions 

 (latitude, longitude and time), as he has shown how to do in the latter part of the paper. 

 I have asked him to send you a copy of it. Very faithfully yours, Francis Galton. 



42, Rutland Gate, S.W. October 8, 1877. 

 Ml dear Professor*, We are now not only nearly but quite "in focus," T think. 

 (1) The fiducial marks: — a scale is cheaply cut. We can try the " web " and if it confuses the 

 picture we can ultimately adopt a simpler plan. (2) Weight, or spiral spring? — whichever the 

 "nstrument maker prefers — (One can't do the equivalent easily with a spring, of lifting up the 

 :ounterpoise). (3) Zenith adjustment: — your plan is the simplest and best. (4) Azimuth: — 

 Allah forbid, that I should propose to carry a theodolite about with each instrument, for the 

 sole purpose of laying down rough azimuth. I was merely thinking of Kew and of fixing in the 

 ground there two or more permanent slabs with fiducial marks, and as there is a meridian line 

 laid down, and a theodolite at Kew, I thought it might be just as well to use them — (It is more 

 important to sight one instrument from the other than to get an exact azimuth). (5) Single or 

 doable camera: — I quite agree to beginning with a single one, though when the clouds are low 

 and drift rapidly, I doubt whether it would be possible to work with a single one. The expense 

 of the box, single or double, will be trifling. Our first attempt is sure to be not over good, and 

 whether we have fitted one or two lenses to our first camera, they will serve again. Neither 

 Deed we lmy a lens on purpose for trial — we could easily borrow one — I could lend one, but 

 perhaps it would be better to get one of a large angular field of view. I would meet you at the 

 Athenaeum on Wednesday if you are disposed and will send me a post-card to say about when. 



Very faithfully, F. Galton. 



42, Rutland Gate, S.W. December 10, 1877. 



My dear Professor*, I went yesterday to Maudsley's place at Clapham Junction, saw 

 him, and ordered three dozen plates and accompanying gear (solutions and dropping bottles) — 

 total cost £1/8/0 or thereabouts. Also, I have written to Kew and find that Whipple the 

 Superintendent understands our proposed photographic requirements. There will be trouble 

 about the theodolite, I find, as none that they have there will admit, he says, of viewing an 

 Object placed vertically below the telescope. (There may prove to be some simple way of 

 lengthening the axis for the occasion, or rather for performing some equivalent process.) 



Thanks for your letter. Uniformity of wind velocity and direction at all altitudes can 

 never I fear be expected, as all balloon ascents have shown the contrary. There will probably 

 be Bome curious effects when the pictures are viewed stereoscopically — as, if the clouds move 

 iu opposite directions at different levels, the plates which must be disposed left and right to 



* Professor G. G. Stokes. 



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