584 



NATURE 



[April 20, 1899 



With regard to those exceptions, it may be worth noting that 

 the two in the minimum series of groups (viz. the group for 

 1856, and that for 1890) occur just about the middle of dry 

 periods in the 35 years' cycle of weather. 



Now, the r,fgime of rainfall is often different in the north and 

 south of this island. A year that is wet in London may be dry 

 in the north, and vice versa. The following figures may throw 

 light on the extent of this. 



Compare the annual rainfall at Greenwich, from 1841 to 1897, 

 with that at Rothesay (X.B.), calling each year with excess of 

 rainfall wet^ and each with deficiency dry. 



We find a distribution as follows : — 

 Gr. wet.\ Gr. dry. \ ,„ Gr. wet.^ Gr. dry.") 

 Roth, wet.y Roth. dry. J '^ Roth, dry./ * Roth. wet. J 'J 



Thus the rainfall has been opposite in character in 27 out of 

 those 57 years (nearly one-half). 



Now, with reference to the sun-spot cycle, it would appear 

 that at Rothesay, it is the years about ma.xinia that tend to be 

 the wetter. I am not at present in a position to treat the 

 Rothesay data as those for Greenwich have been treated above. 

 But let us take the annual rainfall, marking each year as + or - , 

 as that has been above or below the average. Then, taking 

 five-year groups about maxima or minima since the beginning of 

 this century, we get the following tables : — 



M a.\. s-year groups. Wet. Dry. 



1 . 1 804 ... I S02- 1 806 2 3 f. 



2. 1816 ... 1814-1S18 3 2 



3. 1830 ... 1828-1832 3 2 



4. 1837 ... 1835-1S39 3 2 



5. 1848 ... 1846-1850 4 I 



6. i860 ... 1858-1862 3 2 



7. 1870 ... 1868-1872 3 2 



8. 1SS4 ... 1882-1S86 3 2 



9. 1894 ... 1892-1S96 2 3 6? 



Sums. 



26 



13 27 



Thus, in the former case (nine max. groups) there is one 

 valid exception' to the rule of a preponderance of wet years ; 

 while the eight minimum groups .show throughout a prepon- 

 derance of dry years. 



The same thing might be shown with more or less distinct- 

 ness for other stations in the north. 



In the eyes of some, a contrariety in rainfall, like that just 

 indicated, doubtless seems fatal to the idea of sunspot influence. 

 But the best thought in meteorology to-day, if I mistake not, 

 would hesitate to atfirm that it is so. The same influence, 

 indeed, acting under different conditions, may produce different 

 and even opposite efl'ects. 



Discussing the que.stion of sunspots and temperature in his 

 recent admirable " Traite elcmentairede Mcteorologie " (1899), 

 M. Alfred Angot points out that the relation is probably a 

 complex one. "On pourrait concevoir," he proceeds, "que 

 les taches solaires influent, par exemple, sur la position des 

 centres de hautes et de basses pressions, et il .serait alors facile 

 de comprendre que ces deplacements produisissent des vari- 

 ations de temperature d'un certain sens dans une region, d'un 

 sens oppose dans un autre, et nulles enfin dans d'autres encore. 

 II est possible qu"en reprcnant ces etvides dans cet ordre d'idees 

 on arrive a concilier les resultats, contradictoires en apparence, 

 que Ton a obtenus jusqu'ici." The same thing should obviously 

 apply to rainfall. 



Is there any evidence that rain-bringing depressions take, 

 on the whole, a more northerly path across this island (in going 

 E. or N. E. ) about the time of maxima sunspots, and a more 

 southerly path about minima ? Perhaps something of this kind 

 might account for the oppositeness in rainfall we have considered. 



I little 



NO. 1538, VOL. 59] 



My object in this letter, however, is rather to call attention 



to facts than to affirm this or that inlluence as accounting for 



them, and it is possible that further inquiry might dissipate the 



notion that sunspot influence is concerned in those phenomena. 



Alex. B. MacDowall. 



Periodic Tides. 



Under the above heading, Prof. A. W. DulT, in Natire of 

 January 12, describes the character of the periodic tides, or 

 secondary tid,-il undulations, on the eastern coasts of Canada, 

 and offers an explanation for these based upon observations in 

 the Bay of Fundy. Without entering into any discussion of the 

 explanation suggested, I wi.sh to point out that the basis of fact 

 upon which he rests his descriptions for most of the places 

 named, is so meagre and insufficient as to render these 

 dsscriptions quite misleading. 



Prof. Duff has visited St. John in the Bay of Fundy, and has 

 had access to the tide gauge there established by the Tidal 

 Survey. The observations at Quaco and on the St. John river 

 are his own. But with regard to the other places mentioned, 

 his descriptions of the character of the oscillations are entirely 

 based upon a few examples of simultaneous tides, in sets of only 

 four days each, published to illustrate a paper of mine in the 

 7'raiisaclioiis of the Royal Society of Canada, and reproduced in 

 one of the reports of progress of this Survey. These were 

 selected to show the character of the main tides, without respect 

 to the minor undulations. On one illustration it was even noted 

 that the tides there represented were unusually free from 

 secondary undulations which appear as a rule at that station. 

 These few illustrations cannot, therefore, properly be employed 

 as a basis for a comparative description of the usual char- 

 acter of these undulations ; and it is not right to make this 

 use of them when valuable continuous records from recording 

 gauges exist, by which the subject could be investigated 

 thoroughly as it deserves. 



The other places outside the Bay of Fundy named by 

 Prof. Duflf are all tidal stations of this Survey, which is being 

 carried on by the Department of Marine, under my direction. 

 There are eight principal stations in the region, extending 

 from Quebec to Halifax, and from Yarmouth at the south end 

 of Nova Scotia to the Strait of Belle Isle. In this region, 

 which includes the Gulf of St. Lawrence and the Bay of 

 I-'undy, the tides range from the highest in the world to so 

 flat a tide as to be almost inappreciable except at the springs. 

 At these stations, from two to four years of continuous tidal 

 record has already been obtained, accompanied by meteor- 

 ological returns from ten stations in the region, and supple- 

 mented by a complete file of daily weather charts showing the 

 isobars, issued by the Meteorological Service, which is another 

 branch of the Marine Department, .^t three of the tidal 

 stations themselves a barograph record is also secured. The 

 monthly charts issued by the Hydrographic Office of the 

 United States, which show the tracks of all the important 

 storms, are also available for purposes of comparison. In 

 addition to these principal stations, there are now fifteen 

 secondary stations, which have been in operation for three or 

 four months during the summer season in the Gulf of St. 

 Lawrence and the Bay of Fundy, at which simultaneous tidal 

 comparisons have been obtained on recording gauges. 



At some of these stations the secondary undulations are per. 

 sislent and continuous ; at others, they appear about half the 

 time ; while at others again, usually towards the head of 

 estuaries, they seldom (if ever) appear. 



The excellent field thus afforded for the investigation of the 

 question was pointed out in a "Note" on the subject, com- 

 municated by n-x, in May 1895, t° •'"^ Royal Society of Canada 

 {Trans. Roy. Soc. of Canada, vol. i.. Second Series, 1S95-96). 

 The question of the origin of these undulations has been 

 examined by Mr. F. Napier Denison, of the Meteorological 

 staff; his endeavour being to establish a relation with the 

 fluctuations of the barometer. With this in view, he has 

 examined some pan of the tidal record as above, and also the 

 tidal record from our Pacific coast stations. The results of his 

 investigations, as far as he has yet carried them, are published 

 in the Proccidiiij^s of the Canadian Institute, Toronto ; paper 

 read Januarv 16, 1897. lie has also made an investigation of 

 similar short-period undulations in the Great I^ikcs (see Pro- 

 teediiigs Canadian Institute : paper read February 6, 1S97). 

 This, with the references given by Prof. DufT to his own 

 papers, completes the study yet given to the subject in Can.ida. 



