May 26, 1910J 



NATURE 



Z^7 



of thin solid films are next treated, including Quincke's 

 experiments on the range of molecular action. Chap- 

 ter ix. is devoted ■ to the behaviour of homogeneous 

 mixtures, both liquid and solid, and chapter x. to 

 heterogeneous mixtures, such as alloys and mixtures 

 of salts. The concluding chapter concerns colloidal 

 solutions, their preparation, structure, &c. 



The book, as a whole, is very good. It contains a 

 large fund of information, clearly put and in logical 

 order. It is therefore both readable and instructive. 



Aids to Microscopic Diagnosis (Bacterial and Para- 

 sitic Diseases). By Capt. E. Blake Knox. Pp. 

 viii + 156. (London: Bailliere, Tindall and Cox, 

 1909.) Price 2S. 6d. net. 

 This little book is a resume of clinical methods as 

 applied in the diagnosis of bacterial and parasitic in- 

 fections of man, and contains a large amount of 

 useful matter in a small space. It is not meant to 

 take the place of, the ordinar\- text-books on these 

 subjects, but tOjber-used for revision purposes, and 

 will be found handy by travellers who are unable to 

 burden themselves with many books. Protozoal 

 organisms, such as malaria, trypanosomes, and spiro- 

 chaetes, filaria, pathogenic bacteria, and the diseases 

 they cause, pathological secretions, the opsonic index, 

 and vaccine therapy are all dealt with, together with 

 the methods required to demonstrate and isolate the 

 causative organisms. 



We have noticed a few slips and omissions, e.g. 

 the Streptococcus pyogenes is spoken of as the S. 

 Pyogenes aureus; no mention is made of the fact that 

 the Staphylococcus pyogenes group liquefies gelatin, 

 while the Staph, cereus group does not ; it is question- 

 able if the tubercle bacillus can ever be detected in 

 the blood; the term "subtertian," now commonly 

 applied to the malignant form of malaria, is not 

 mentioned; toxin and not dead culture is used for 

 the preparation of diphtheria antito>Lin ; prophylactic 

 vaccination in cholera is j^iven undt-i the heading 

 "■'scrum therapy," &c. Within the limitations stated 

 by the author, we think a useful purpose will be 

 served by this little book. R. T. Hewlett. 



Lift-Luck on Southern Roads. By Tickner Edwardes. 



Pp. XV + 30 1. (London : Methuen and Co., 19 10.) 



Price 6s. 

 Here is a pleasantlv written description of a journey, 

 of some two hundred miles, through five southern 

 English counties, on an unusual plan. Mr. Edwardes 

 says, " My plan consisted in waiting by the roadside 

 or strolling gently onward, until something on wheels, 

 it mattered not what, overtook me ... by dint of 

 laving under use the whole gamut of country- peram- 

 bulation, at length, after many days of travel, I 

 found mvself at mv journey's end." Having only a 

 camera and a pack, the author was able to go into 

 every byway he fancied and investigate any subject 

 which presented itself. His account of his wander- 

 ings and his illustrations will delight all lovers of the 

 country. 



Praenunciae Bahamensis. II., Contributions to a 

 Flora of the Bahamian Archipelago. By C. F. Mills- 

 paugh. (Chicago : Field Museum of Natural 

 History, 1909.) 

 This is the second fascicle of a contribution to a flora 

 of the Bahamian Archipelago, issued by the Field 

 ^luseum of Natural Histon.-. It contains observa- 

 tions on old species, the establishment of the new 

 genus Euphorbiodendron. and the description of 

 eleven novelties distributed among the genera Dondia, 

 Portulaca, Chamaesyce, Croton, Centaurium, Helio- 

 tropium, Varronia. Catesbaea, and Callicarpa, col- 

 lected in fifteen different islands of the group. 



NO. 21 17, VOL. 83] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, refected 

 manuscripts interuied for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



Halley's Comet and Magnetic and Electiical 

 Phenomena. 



Halley's comet has been a source of interest to 

 magneticians as well as to astronomers. The question was : 

 Would the proximity of the comet's tail occasion a mag- 

 netic storm or would it not? If the tail consists of elec- 

 trified particles, and if it were to envelop the earth, then 

 a magnetic storm appeared a reasonable concomitant. It 

 was thus with some expectancy that I consulted the 

 magnetic curves recorded at Kew on May 19. The con- 

 clusion that will be drawn from these and similar records 

 will, I suspect, depend somewhat on the temperament of 

 the inquirer. .\ large magnetic storm unquestionably there 

 was not, but there was disturbance. 



The position may perhaps be best explained by reference 

 to the international lists that are published as to the mag- 

 netic character of individual days. Days are classed as 

 "o," " I," or "2," according as they are magnetically 

 quiet, moderately disturbed, or highly disturbed. Taking 

 the three years 1906, 1907, and 1908, the Greenwich and 

 Kew lists, while differing in details, agreed in putting 

 39 per cent, of all the days in class " o," 585 per cent, 

 in class '* i," and 25 per cent, in class " 2." No day 

 practically is absolutely quiet, and a good many days are 

 so near the line of demarcation of classes " o " and " i " 

 that it is a good deal a matter of chance to which they 

 are assigned. Again, there are an appreciable number of 

 days so near the common margin of classes " i " and *' 2 '* 

 that they may well be assigned to either. Thus while the 

 Kew and Greenwich lists for the three years mentioned 

 each assigned twenty-nine days to class '' 2," onlj- nine- 

 teen days were common to both lists. If, then, a day is 

 chosen by haphazard, it is most likely to be of disturbance 

 class '' I," while the odds against its being of class " 2 " 

 arc not so great that if it should prove to be of that class 

 one is compelled to accept the coincidence as necessarily 

 more than accidental. 



In the present instance what was a priori the most 

 probable event has happened ; May 19 was undoubtedl}- of 

 disturbance class " i." So far, indeed, as the declination 

 curve was concerned, the choice between classes *" o " and 

 " I " was not ver>' clear, but the horizontal force cur\-e — 

 while very far from being highly disturbed — was un- 

 questionably up to the average class " i " level. The most 

 rapid horizontal force changes occurred between 10 a.m. 

 and noon, the range of the largest oscillation being about 

 507 (0*0005 C.G.S.). There were also changes of nearly 

 the same size between o and 2 a.m., and again between 

 3 and 5 p.m. The largest irregular declination movements 

 occurred between o and 3 a.m., the range being about 9'. 

 Later in the day there were some oscillatory declination 

 movements synchronous with those shown in the horizontal 

 force cur\'e, but their amplitude was only 2' or 3'. 



As a rule, days of class " o " and days of class " 1 " 

 disturbance occur in groups. The present occasion follows 

 the general rule. From May 13 to 20 no day, except 

 possibly May 16, was of class " o." May 13 being the 

 most disturbed. There were horizontal force changes on 

 the afternoons of May 17 and iS similar in size to those 

 on May 19. The afternoon of May 20 was also disturbed, 

 though less so. The disturbances on May 18 and 19 were 

 similar in magnitude to those which in 1902-3 accompanied 

 what Prof. Birkeland termed " polar elementarv " mag- 

 netic storms in the .Arctic, and if Prof. Birkeland expected 

 no more than a " polar elementary " storm from the 

 passage of Halley's comet, then I have little doubt that 

 the special observations he has been making in the Arctic 

 will have supplied him with what he was looking for. 



As it was conceivable that the intrusion of a comet's 

 tail into the earth's atmosphere might exert a visible effect 

 on the electric potential, I have also examined the Kew 

 electrograms. The electrograms from May 19 to May 20 



