February 1, 1898.; 



KNOWLEDGE. 



33 



%ttttxs. 



[The Editors do not hold themaelTes reaponsible for the opinions or 

 statements of correspondents.] 



IS WKATHER AFFKCTKD UV THK MOON :- 

 To the Editors of Knowledge. 

 Sirs, — I Lave been reading with much interest the 

 article with the above title by Mr. A. B. MacDowall, M.A. 

 There is one diliiculty in connecting the barometric curves 

 with the moon's age and position which he appears to have 

 overlooked. It is this. His map of the curves is for 

 London, but taking the meridian of London, and proceeding 

 north or south, the pressure varies greatly on the same day. 

 Thus there may be very high readings in London, whilst 

 very low ones prevail over Scotland and the South of 

 France, or vice versa, according to the position of anti- 

 cyclones or storm centres. 



The same may be said regarding places having the same 

 latitude. Storms cross the Atlantic in about a week, 

 though they vary much in their rate of progress and the 

 direction in which the centre of the cyclone advances. 

 May not this be influenced by the increase or decrease of 

 the moon's declination ? If this is so, it would help to 

 explain much which is obscure in the way the moon affects 

 the weather. 



Near the Equator one would expect to find evidence of 

 any change of pressure caused by the moon's attraction, 

 as twice monthly it passes directly over those regions. 

 This, however, does not seem to be the case. In Southern 

 India the barometer readings scarcely vary for months, 

 excepting the daily tides, and a slight fall during the south- 

 west monsoon. 



The spread of this monsoon and the rainfall which 

 accompanies it in Northern India has, I believe, been 

 supposed to be affected by the moon's action, but I do not 

 know on what data. During the monsoon there are 

 usually breaks at intervals of about a fortnight, which 

 would tend to support that theory. L. Paxton. 



Lavant, Chichester. 



[I did not overlook the point raised as a difficulty by 

 Colonel Paxton. While I rather think the smoothed 

 Greenwich curve might be taken as fairly representative 

 for a considerable region (perhaps the greater part of these 

 islands), I should not be surprised to find at some more 

 distant stations either (1) an equally good correspondence, 

 but with the waves retarded or advanced somewhat, or even 

 opposite in phase to the Greenwich waves ; or (2) a corre- 

 spondence imperfect or obscured, or no proper corre- 

 spondence at all. In the former case the evidence of 

 lunar influence would, I consider, be strengthened, and 

 in the latter I do not see that it need be seriously shaken. 

 In a science so little advanced as meteorology, and dealing 

 with such a " complex " of natural causes, we should be 

 extremely chary, I think, about asserting what should or 

 should not happen in this place or that on the hypothesis 

 of some influence of astronomical nature. Our business 

 as students of natural law is primarily with facts, and the 

 interpretation of facts. And in the weather of any region, 

 it seems to me, we may find so large an amount of regular 

 correspondence with some astronomical cycle (that of the 

 moon, e.f/.), that it becomes more difficult to think all this 

 agreement purely fortuitous than to believe there is a 

 causal nexus between the phenomena. I do not assert 

 it is so in the present case, though I may be inclined to 

 hold it as a " pious opinion." If we find a good corre- 

 spondence in one region and not in another, may there 

 not be something in the peculiar position of the former 

 region which tends to render the supposed influence 



apparent ? And, similarly, if we find a good corre- 

 spondence in certain years and not in others, may we not 

 find this due to something special in the relative positions 

 of the moon and the earth in the former case ? Colonel 

 Paxton's suggestion that the path of depressions may be 

 influenced by the moon's declination seems to be well 

 worth consideration. — Alex. B. MacDow.u.l.1 



To the Editors of Knowledge. 

 Sirs, — With reference to the article in your issue for 

 January this year, entitled "Is Weather afl'ected by the 

 Moon ? " may I be permitted to make a few remarks ? As 

 the writer states, the periods of concurrence between the 

 barometrical curves and the various phases of the moon 

 are irregular ; or, to put it otherwise, he sometimes 

 observes that they coincide. Si post hoc, non enjo prapter 

 hoc, is an excellent maxim in meteorology, as in other 

 things. R. A. Proctor, in an essay called " Sunspot, 

 Storm, and Famine," says as follows : " That for countless 

 ages the moon should have been regarded as the great 

 weather-breeder, shows only how prone men are to recog- 

 nize in apparent changes the true cause of real changes, 

 and how slight the evidence is upon which they will 

 base laws of association which have no real foundation m 

 fact. . . . And as the weather is always changing, even as 

 the moon is always changing, it must needs happen that 

 from time to time changes of the weather so closely follow 

 on changes in the moon as to suggest that the two orders 

 of changes stand to each other in the relation of cause and 

 effect. Thus rough rules came to be formed ; and as (to 

 use Bacon's expression) ' men mark when such rules hit, 

 and never mark when they miss,' a system of weather-lore 

 gradually comes into being which, while in one sense 

 based on facts, has not in reality a particle of true 

 evidence in its favour — every single fact noted for each 

 relation having been contradicted by several unnoted facts 

 opposed to the relation." 



Furthermore, I would like to know if pressure alone 

 constitutes weather ? G. E. E. 



January 16th, 1898. 



[While it is well to remind ourselves of the tendency 

 above spoken of, the applicability of Proctor's remarks to 

 the present case may fairly, I think, be doubted. We 

 have to account for a barometric rhythm (similar to the 

 lunar), persisting for the greater part of a year at one time. 

 I have not represented that " pressure alone constitutes 

 weather." — Alex. B. MacDow.\ll.1 



VEaETATIOiV OP AUSTRALASIA. 

 To the Editors of Knowledge. 

 Sirs, — It is with some diffidence that I again venture 

 to trespass upon your valuable space, but I can hardly 

 allow Mr. W. B. Hemsley's remarks upon my letter in the 

 September issue of Knowledge to pass unchallenged. It 

 seems absurd to me — as it must also to anyone who read 

 Mr. Hemsley's article in the May issue of this journal — 

 that he should deny having written the statement I attri- 

 buted to him, and accuses me of not having read the 

 opening sentence carefully. In this Mr. Hemsley errs, 

 for I read and re-read it, as I could scarcely credit my 

 senses after a first perusal that a botanist of Mr. Hemsley's 

 world wide reputation could be guilty of such a misstate- 

 ment. Mr. Hemsley twits me with making a general 

 statement re the genus Ficus, and characterizes it as mis- 

 leading ; it would have been an easy matter to have cited 

 the forty species of this genus, but cui bono ? If I may 

 make the retort, Mr. Hemsley is still more misleading in 

 his statements. " The Vegetation of Australasia " is the 

 subject of his paper. Queensland forms a large part of 



