HISTORY OF THE WORK. XXV 



for a short time only/ and might be somewhat modified by making use of a longer 

 series of observations. It is probable, moreover, as I have shown elsewhere, that 

 Sitka lies without the zone of westerly winds, and where a different law may pre- 

 vail. 



" 3d. That the line of its approach generally makes an angle, more or less acute, 

 with one drawn to the point of maximum pressure.^ The only exception is at 

 Hamilton,^ Bermuda, where it is slightly obtuse (92° 40'). Nor is the result 

 different, if, instead of regarding the mean resultant of all the forces which raise 

 the barometer as the point of maximum pressure, we (perhaps more properly) 

 regard each fall as a negative rise, and vice versa, and then obtain one mean re- 

 sultant for the whole. The fourth column in Table II. was computed in this way, 

 and the results are shown on the Barometrical Wind-roses [Plate 23] by a broken 

 line. [For application of this discussion to the storm-curve, see author's article 

 on pp. 89-101, Proceedings of the American Association for the Advancement of 

 Science, Cleveland, Ohio, 1853.] 



"The plan of the 'Winds of the Globe' contemplated giving resultants at each 

 place, for each month and season, with monsoon influences for the seasons. The 

 work would be much more perfect, if this could be done in all cases, but the 

 magnitude of the labor forbade it. For a like reason, as well as to render it 

 possible to represent the results on maps, it was thought judicious to group the 

 places of observation by districts, where they were numerous, instead of making 

 computations for each place separately. With the facilities we have devised, in 

 the way of special tables to aid in the computations, we have found that where 

 observations, recorded for 16 points of the compass, have been collected and pro- 

 perly arranged for computation, an active computer can calculate about 35 resultants 

 in a day. When the observations are recorded for 32 or more points of compass, 

 the labor is of course much greater, but there are comparatively few such. On 

 the other hand, there are many where they are recorded for only 8 points. If we 

 include the calculation of the monsoon influences, Avhich has been done chiefly by 

 plotting, the average per day will not exceed the number just named." 



[The exact state of forwardness of the work at the time of Professor Cofiin's 

 decease is fully related in the preface.] 



' One month at Sitka, and two at Barnoule. 



' Further on, in the same article from which these conclusions are quoted, and which may be 

 found on page 89 of the Proceedings of the American Association for the Advancement of Science, 

 1853; Prof. Coffin determines this angle as 65°; and a reference to the article plainly shows that 

 this determination was reached, without any knowledge by him of its having been accomplished, or 

 even attempted, at that time, by any other writer on the subject, although the reference on page 

 664, of this work, conveys the intimation that this principle is generally referred to in Europe as 

 "Buys-Ballot's Law of the Winds". But it does not there appear at what date Prof Ballot 

 had made the announcement, with which he is so accredited. 



' It is worthy of remark that here, too, the angle is acute, if, instead of the mean direction of the 

 wind observed at Hamilton, we employ that at Ireland Isle, another island in the same group, or even 

 the mean between the two. 



D December, 1875. 



