February 2, 1917] 



SCIENCE 



115 



pine should be regarded as applicable to either 

 Chimaphila corymhosa Pursb., or C occiden- 

 talis Eydb., the two species into which C. um- 

 hellata Kutt. has been split up in the " North 

 American Flora." 



There is, of course, room for discussion as 

 to the best method of procedure to adopt. 

 Many botanists — especially those who are 

 never called on to name plants for the general 

 public — are quite satisfied with the Latin 

 names alone, and from them in all probability 

 no assistance can be expected in devising Eng- 

 lish names. The subject is one that might well 

 be discussed at some conference of American 

 botanists, as it mainly concerns ourselves 

 alone. J. Adams 



Central Experimental Farm, 

 Ottawa, Canada, 

 November 21, 1916 



PROPULSION BY SURFACE TENSION 



To THE Editor of Science: In November, 

 1911, I described in your columns a little 

 motor boat which I supposed to be novel. A 

 wooden boat only a couple of inches long, 

 was provided with a stern consisting of a slab 

 of soap, and when placed on clean still water 

 moved about with noticeable rapidity. 



I have just learned that M. Henri Devaux 

 constructed an absolutely equivalent craft 

 many years ago (La Nature, April 21, 1888). 

 His boat was made of tinfoil and the " pro- 

 peller " was a scrap of camphor attached to 

 the stern. 



Pray allow me to tender to M. Devaux my 

 apologies and compliments. 



George F. Becker 



SCIENTIFIC BOOKS 



A Sylow Factor Taile of the First Twelve 

 Thousand Numbers. By Henry Walter 

 Stager. Carnegie Institution of Washing- 

 ton, 1916. Pp. xii+119. 

 Dr. Stager's tables are intended to furnish 

 the possible number of Sylow subgroups for 

 all groups whose order does not exceed 12,000. 

 For every number within that limit are listed 

 all the divisors which are of the form 

 p(kp + l), where p is a prime greater than 2 



and k is greater than zero. In determining 

 the possible number of Sylow subgroups such 

 divisors must be known before further meth- 

 ods are applicable. Thus from the table we 

 learn that 1,080 is divisible by 3(1X3 + 1), 

 3(3X3 + 1), 3(13X3 + 1), 5(1X5 + 1), 

 5(7X5 + 1) and 5(43X5 + 1). From these 

 results we know that for a group of order 

 1,080 there may be 1, 4, 10 or 40 subgroups of 

 order 3^ and 1, 6, 36 or 286 subgroups of order 

 5. The exact number is to be determined by 

 other principles of group theory. The table 

 also gives the expression of each number up 

 to that limit as products of powers of primes. 



The making of tables, a tedious and appar- 

 ently mechanical task, is of the highest impor- 

 tance in all branches of science. It is likely 

 that more fundamental theorems have been 

 discovered by the examination of listed results 

 than by any other means. This is certainly 

 true in the theory of numbers, and it is pos- 

 sible that workers in the theory of groups have 

 not made enough use of this method of inves- 

 tigation. The construction of tables for the 

 theory of groups is especially difficult on ac- 

 count of the great complexity of the material. 

 Only brief tables have hitherto been und'wr- 

 taken and it is to be hoped that Dr. Stager's 

 work in this direction may be the beginning 

 of a systematic campaign in this important 

 field. 



The construction of an extensive table al- 

 most always brings to light hidden relations, 

 suggesting new theorems for investigation. 

 In Dr. Stager's table certain numbers are 

 noted which have no divisors of the sort indi- 

 cated above. Such numbers seem to resemble 

 primes in many ways, and in particular their 

 " curve of frequency " seems to run roughly 

 parallel to the corresponding curve for primes. 

 Dr. Stager has made a study of these numbers, 

 and has added a list of them up to the limit 

 of his table. 



The author is to be congratulated upon the 

 completion of so important and formidable a 

 piece of work. While the reviewer has, of 

 course, not checked over any part of the table 

 he has the utmost confidence in the accuracy 

 of the list. The printing has been done by the 



