220 



NATURE 



[October 29, 1914 



for the estimation of the radioactivity of mineral 

 waters. A considerable amount of attention is 

 paid to the biological, as distinguished from the 

 bacteriological, examination, and a large number 

 of excellent figures are given of tlie various species 

 of organisms likely to be met with in waters of 

 various types. 



The least satisfactory section is that dealing 

 with the bacteriological examination of water. In 

 particular, the detection and enumeration of the 

 ii. coli communis, to which so much attention is 

 paid in this country, is treated in an extremely 

 madequate manner. 



Highways and Byways in Lincolnshire. By W. F. 



Rawnsley. With illustrations by F. L. Griggs. 



Pp. XX + 519. (London: Macmillan and Co., 



Ltd., 1914-) Price 55. net. 

 This book maintains the high reputation of the 

 series to which it belongs. Mr. Rawnsley has 

 throughout supposed the tourist to be travelling 

 by motor, and has accordingly said very little 

 about footpaths. Lincolnshire, he says, teems 

 with splendid churches, and that is the first im- 

 pression received after looking at the admirable 

 illustrations which Mr. Griggs has provided. But 

 attention is by no means confined to ecclesiastical 

 architecture, for the book abounds in anecdotes, 

 gossip, and quaint information. We read that 

 Sir John Franklin, the famous arctic navigator, 

 and Major James Franklin, who made the first 

 military survey of India, were born at Spilsby 

 in this county. On the road from Spalding to 

 King's Lynn the author tells us he passed' a field 

 with an unfamiliar crop of stiff purplish plants 

 which showed where the cultivation of Isatis 

 tinctoria, the woad plant, which added so much 

 to the attractiveness of our earliest British an- 

 cestors, was still kept going. Or, again, at 

 Tothby a plague-stone is to be found, and we 

 are given a bright account of how sufferers from 

 the plague in the seventeenth century were fed 

 without spreading infection. The book will appeal 

 not only to Lincolnshire people, but also to all 

 who love the English countryside. 



Les Coordonncs intrinseques. Theorie et Appli- 

 cations. By Dr. L. Braudc. (Scientia, No. 

 37.) Paris : Gauthifer-Villars, 1914. Pp. 100. 

 Price 2 francs. 

 Although quite good in its way, this book does 

 not present any very striking features. It may 

 best be described as a collection of problems most 

 of which could be worked out as exercises by 

 any fairly good English mathematical student. 

 Intrinsic equations are here obtained for the usual 

 well-known plane curves, such as cycloid, 

 catenary, equiangular, spiral, and they are applied 

 to the study of associated loci such as roulettes, 

 Mannheim's curves, pedals, or involutes and 

 evolutes. In England this work is commonly 

 studied in courses rightly or wrongly described 

 as "advanced calculus," but it may be useful to 

 teachers and others to have a book of reference 

 in which the svibject is treated separately and in 

 greater detail than in our calculus text-books. 



NO. 2348, VOL. 94I 



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, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.} 



Accumulated Rainfall at Excessive Rates. 



I.\ the Monthly Weather Review a table (No. II.) 

 is regularly published giving accumulated amounts of 

 precipitation when the rates equal or exceed : — 



Duration 5 10 20 30 60 minutes. 



Rate per hour 300 i-8o 1-20 100 080 inches. 



Unfortunately the headings and the entries are not 

 consistent ; and the purpose of the table is defeated 

 by a tabular arrangement in which sense is sacrificed 

 for space. The table misleads American meteoro- 

 logists, even those of us familiar with the arrange- 

 ment ; and it is therefore not to be wondered at that 

 the most eminent of climatologists, Dr. Julius v. 

 Hann, read for a five-minute interval 419 in. of rain 

 when the actual fall was 013 in. at Oklahoma, June 

 30, 1913 {j\LW.R., 417: 1129, July, 1913). 



Prof. Hann directed attention in the Meteor. Zeit- 

 schrift, of which he is editor, to this remarkable rate 

 (Meteor. Zeits., vol. xxxi., part 4, p. 196), stating that 

 it was the heaviest rainfall on record, and gravely 

 adding that the rate, 21-3 mm. was most remarkable, 

 and that it was scarcely conceivable that so much 

 water could fall from the sky in five minutes. 



Dr. Hann should not be held responsible for the 

 error. A correction has been published in a recent 

 number of the review, but few will see it, and in the 

 confusion incident to the war it may escape genera? 

 notice. We are likely, therefore, to meet the state- 

 ment in years to come that official records show a 

 rainfall of the rate given above. 



With the hope of preventing future misunderstand- 

 ings, I have appealed to the chief of the Weather Bureau 

 to alter the table, and have further urged that now 

 is an opportune time to abandon the use of inches in 

 measurements of precipitation and use the millimetre- 

 Is it not also high time that British rainfall was 

 expressed, if not indeed measured, in millimetres? 



Accumulated amounts at excessive rates are of in- 

 terest to engineers, and it might be well to substitute 

 for the present values, which are arbitrary and con- 

 fusing, the following rational units : — 



Duration ... i 5 10 60 minutes. 



Rate per hour ... i 5 10 20 mm. 



I add the heaviest known rainfalls and rates with 

 the hope that some of the readers of X.^ture will 

 amend. 



Rate per Actual du-ation 

 hour of rate 



Baguio, P. I., July lA, 1911 ... 49 mm. 24 hours 



Campo, Cal., August 12, 1891 ... 219 „ 80 minutes 



Guinea, Va., August 24, 1906 ... 470 ,, 30 „ 

 Curtea de Argrea(Roumania), 



July 7, 1889 615 ,, 20 „ 



Alexander McAdie. 

 Blue Hill Observatory-, October 12. 



Fizeau's Experiment and the Principle of Relativity. 



Sir Joseph Larmor has kindly pointed out to me 

 that it is incorrect, in the interpretation of Fizeau'< 

 experiment, to assume that the velocity of propagation 

 of light is the group velocity, so that l must withdraw 



