June 15, 1916] 



NATURE 



321 



logfarithms, natural sines and tangents, specific 

 gravity and hydrometric tables, and tables of 

 solubilities of a wide range of substances. As a 

 rule, care has been shown in selecting the latest 

 and best authorities, and the whole has been put 

 together in a convenient form. The proofs have 

 evidently been very well read, as the book is 

 remarkably free from typographical errors. The 

 editor deserves great praise for the thoroughness 

 with which he has done his work, and the book, 

 we trust, will find a place in the laboratory or on 

 the desk of every chemical consultant. 



The Purpose of Education: An Examination oj 

 the Education Problem in the Light of Recent 

 Psychological Research. By St. George Lane 

 Fox Pitt. New Edition. Pp. xxviii + 144. 

 (Cambridge: At the University Press, 1916.) 

 Price 2S. 6d. net. 

 Few people, it is to be feared, even among 

 teachers, ever really face the question : ' ' What 

 ought education to aim at?" This book will at 

 least stimulate to such inquiry', and it points the 

 way in the right direction. The author, accept- 

 ing the new conception of human personality 

 which psychical research has brought about, con- 

 siders that the proper purpose of education is 

 the harmonising of psychic phases, the study of 

 the laws governing them, finding their interpre- 

 tation in the art of living and "giving them syn- 

 thetic expression in the growth of character." 

 To put the matter in definite form, the manu- 

 facture of noble souls is the right aim, and the 

 right method is the inculcation of high ideals. 

 The Sermon on the Mount Is the acme of truth 

 and beauty. It urges us to rely less on the seen, 

 the concrete, the physically tangible, and more 

 on the spiritual side of our natures, unmanifest 

 to our senses, but very real and permanent, eternal 

 while the other is temporal. Thus we gain true 

 security and everlasting peace. The present state 

 of Serbia, Poland, and Belgium shows what is 

 the result when education in a neighbour-State 

 becomes materialistic, aiming only at physical 

 efficiency and power. The war has Its lessons : 

 we must learn them. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed &y 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 ationymons cotnmunications.] 



Gravitation and Temperature. 



As the outcome of a very delicate systematic series 

 of experiments (Phil. Trans., 1916) it is announced by 

 Dr. P. E. Shaw that " when one large mass attracts 

 a small one the gravitative force between them in- 

 creases by about 1/500 as temperature of the large 

 mass rises from, say, 15° C. to 215° C." ; that is, it 

 increases by about 1-2 x 10-' of itself per degree Centi- 

 grade. This seems to be a very startling result, at 

 any rate if temperature is merely the expression of 

 internal molecular motions, as, indeed, Dr. Shaw 

 seems to admit. 



By Newton's principle gravitation between masses 



NO. 2433, VOL. 97] 



must act reciprocally ; the result, therefore, means that 

 the astronomical mass of a body must increase with 

 temperature by 1-2x10-* of itself per degree Centi- 

 grade. The pendulum experiments of Bessei and re- 

 cent determinations by Ebtvos seem to establish pro- 

 portionality between gravitational mass and mass of 

 inertia, irrespective of temperature, well beyond these 

 limits. Thus inertia also would have to increase with 

 temperature; and when a freely moving mass is 

 becoming warmer its velocity must be diminishing, 

 for its momentum must be conserved. A comet like 

 Halley's is heated upon approach to the sun; thus it 

 should suffer retardation in the approaching, and 

 acceleration in the receding, part of the orbit, enough 

 probably to upset existing astronomical verifications. 

 Indeed, as regards change of inertia, we can recall 

 the principle applied by Prof. Joly to the question 

 whether chemical change involves change of mass, 

 viz., that every mass around us is moving through 

 space with the velocity of the solar system, and a 

 sudden rise of temp>erature In a body must therefore 

 involve a violent kick if its inertia is thereby sensibly 

 altered. 



Electrodynamic theory does establish unequivocally 

 an increase of inertia of a body arising from gain (SK) 

 of thermal or electric energy; but this is only of 

 amount SE Ic-, where c is the velocity of radiation, and 

 so is minute beyond detection. The question whether 

 there is also an equivalent increase in gravitational 

 mass evades discussion until some link connecting 

 gravitative and electric forces has been established. 



J. L. 



Cambridge, June 5. 



A Plague of Caterpillars. 



With reference to what has appeared in the public 

 Press relative to the devastation caused by caterpillars 

 to the oak trees at Ashtead, you may be interested to 

 know that some three or four years since a sirnilar 

 occurrence took place in the oak plantations in Rich- 

 mond Park. 



The denudation of the trees was so severe that in 

 the spring of 1913 H.M. Office of Works consulted 

 Mr. Maxwell Lefroy, the famous entomologist of the 

 Royal College of Science, with the view of stamping 

 i out the pest. Eventually it was decided to spraj- the 

 trees with chromate of lead at such a time that the 

 5-oung caterpillars, on hatching out, should have only 

 poisoned food. The spraying operations were carried 

 out bv portable high-pressure pumping apparatus 

 loaned by myself, self-supporting telescopic ladders 

 being provided to reach the tree-tops some 40 ft. from 

 the ground. 



This was, I believe, the first occasion on which 

 attempts were made to spray such large trees, and 

 there is not much doubt that the oaks at Ashtead 

 could be treated in a similar manner. 



It is, of course, now too late in the season to 

 undertake preventive measures, but if spraying were 

 undertaken early next Mav I have not much doubt 

 that the pest could be eradicated. 



J. CoMPTOx Merry WEATHER. 



4 WTiItehall Court, S.W., June 7. 



The Black-eared Wheatear: A New Bird for the 

 Irish List. 



Ornithological readers of Nature will no doubt 

 be interested to learn that a black-eared wheat- 

 ear (CEnanthe hispanica) was obtained on Tuskar 

 Rock, Co. Wexford, on May 16, b}' Mr. Glan- 

 ville, principal lightkeejjer. There are two races 

 of this bird, an Eastern and a Western, each 

 of which exhibits dimorphism of plumage, the 



