TraiiKitloH StmltiH ;')5 



l)efore thu arrival of the centre of jjreatest disturluiiice. Accordingly (>alton 

 reaches a formula of the form 



//,-/i, = mh(12)-v,(liJ)}+/>{<,(12)-<.(12)}+7H(l2)-c/.(l2)}, 



where /t = pressure, i'(l2) e<]ual average wind-velocity, <(12) eq«ial average 

 temperature and d{\'l) equal average damp for 12 houi*H round an epoch, 

 and the subscripts 1 and 2 re[)re8ent epochs of time at a few hours interval. 

 Galton then determines in rough figures the values of in, p, (j from observa- 

 tions at Falmouth. So far he might — by very crude methods indeetl — be 

 determining a multiple regression formula. Hut the next step he takes i« 

 erroneous; he transfers what amounts to v, to the other side of his equation, 

 and proceeds to predict v.. from Ixirometric height, etc. It wiw not till much 

 later that (Jalton realised that in the simplest amu the prediction formula 

 of V from h is not the same formula as that of A from v. Hence although his 

 conclusion that average wind-velocity cannot l)e closely predicte<l from baro- 

 metric height is true, his method really failed to demonstrate it rigidly. 



"The barometer when consulted by itself, without a knowledge of the weather at adjacent 

 stations, can cluini but one merit, nitmoly, to guide us in a form of storm which does not occur 

 once a year in tin- Hritisli Isles, of iv fall in the mercury out>st ripping in an extraordinary (h-gree 

 the increasing severity of the weather; Jind I Ix-lieve it to be on account of this rare phenomenon 

 here, and of the reports of sailoi-s from hurricane latitudes, where it is much more frequent, that 

 the fanie of the instrument ha.s been so widely spread." 



With his usual instinct Galton had reached a true conclusion, although 

 his method was at fault. For us the interest of his paper lies in the evidence 

 that he was feeling his way towards 'correlation''. 



A series of three papers nuist now be considered in conjunction. The 

 earliest of these is entitled : "On the Conversion of Wind Charts into 

 Passjige Charts." It was read in Section A of the British Association, 1866 

 {Tran,s. Sections, pp. 17-20), and published also in the Philosophical 

 Magazine, Vol. x.vxii, pp. 345-8, 1866. Galton explains his purpose in 

 the following words: 



''The most direct ]in(! between two points of the ocean is seldom the quickest route for 

 sailing vessels. A compromise has always to be mode l)etween directness of route on the one 

 hand, and the best chance of propitious winds and currents on the other. Hence it is justly 

 argued that an inquiry into the distribution of the winds over all parts of the ocean is of high 

 national importance to a seafaring people like ourselves. A knowledge of the distribution of 

 the winds would clearly enable a calculation to be made which would show the most suitable 

 passage in any given case'''. But as a matter of fact, no calculations have yet l)een made upon 

 this base; much less have charts Ijeen contrived to enable a navigator to estimate by simple 

 measurements the prol)able duration of a proposed voyage. The wind charts compiled by the 

 Meteorological Department of the Board of Trade are seldom used by navigators; for they do 



' Galton's paper le<l to a long correspondence with G. H. Darwin (afterwards Profe8(K»r 

 Sir George Darwin), chieHy nott^worthy becaiuse from this date an intimate correspondence 

 sprung up and touched many other problems that Galton was considering in later years. 



t" Galton was clearly endeavouring to replace the straight lines and loxodromes of Mercator's 

 Chart by a modern tlKH)ry which should take account of the variations of the wind— less suited 

 indee<l to the examination room, but of more practical value. How few Cambri i rnatical 

 examiners appear to have realised even since Galton s time the futility of K'\ , which 

 



