4*4 



NA TURE 



[March 22, 1906 



tion both in the text and in the diagrams. There 

 are chapters on the nature of sound, waves of sound, 

 musical scales, organ pipes, " time " and movement, 

 the ear, and the voice. Nothing could be happier 

 than the exquisite drawings by Miss Martin Mohun 

 showing an ideal couple — a boy and girl — waltzing 

 and drawing sound curves on the seashore. Mr. 

 Lapidge's diagrams are also excellent. To assist the 

 teacher six models, made by Mr. Lapidge, may be 

 obtained for the illustration of the book for one guinea. 

 These models show the structure of the middle ear 

 and the chain of bones. They are accurate in all 

 anatomical details. The box also contains a nightin- 

 gale pipe, which is in miniature an adjustable stopped 

 organ-pipe. Mr. Edmunds has succeeded in showing 

 how science may be made interesting to young people. 

 There is a constant appeal to observation and experi- 

 ment, and the whole subject is treated in such a way 

 as to promote the healthy development of the mental 

 faculties in early life. John G. McKendrick. 



Historical and Modern Atlas of the British Empire, 

 specially prepared for Students. By C. Grant 

 Robertson and J. G. Bartholomew. Sixty-four 

 plates. (London : Methuen and Co., 1905.) Price 

 4>\ bd. net. 

 Philips' Model Atlas. Fifty Maps and Diagrams in 

 Colour. (London : George Philip and Son, Ltd. 

 11. d.) Price 6d. net. 



The first of these atlases is full of material de- 

 signed to show students and teachers how intimately 

 the studies of geography and history are related. The 

 excellently executed plates serve as graphic object- 

 lessons demonstrating the interdependence of cause 

 and effect, and are skilfully conceived with a view to 

 impress various important lessons pictorially. The 

 atlas may be commended to the careful attention of 

 both teachers of geography and history. 



The sixpenny atlas of Messrs. Philip gives great 

 prominence to photographic relief maps of the 

 countries dealt with, and these plates will prove of 

 great assistance in enabling young pupils to form 

 mental pictures of the distribution of highlands and 

 lowlands in the countries they are studying, thus 

 providing them with a means to understand the 

 direction of flow of rivers, the distribution of rain- 

 fall, and other important geographical features. 

 This wonderfully cheap atlas deserves to be used 

 widely in junior classes. 



Natural Science in Hygiene, or the Life-History of 

 the Non-Bacterial Parasites affecting Man. By Dr. 

 James Rodger Watson. Pp. vi + 62. (Bristol: 

 John Wright and Co. ; London : Simpkin, Marshall, 

 Hamilton, Kent and Co., Ltd., 1905.) Price is. 6d. 

 net. 

 It is stated in the preface that this little book is in- 

 tended to place before the student of public health, in 

 a convenient and realistic way, the life-histories of 

 those members of the vegetable and animal kingdoms 

 which by their mode of life are of importance from a 

 public health point of view, and with which he is ex- 

 pected to make himself familiar. 



If by " student of public health " is meant the med- 

 ical man who is going to devote his life to public 

 health, the details given, though on the whole fairly 

 accurate and up to date, are far too meagre and in- 

 adequate to be of much service, but the diagrams of 

 life-cycles of the parasites discussed may serve to 

 impress the facts on the memory. The book seems 

 to be more suited to the requirements of the sanitary 

 or meat inspector or health visitor than of the student 

 of hvgiene. R. T. Hewlett. 



NO. 1899, VOL. J3~\ 



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.] 



A Plea for Absolute Motion. 

 The title of Prof. Schuster's letter is somewhat wider 

 than its contents. The writer does not discuss whether the 

 term " absolute motion " is significant, but only whether, 

 assuming that the words have a definite meaning, the 

 absolute motion of any body can be determined by physical 

 inquiry. By implication he has himself answered the 

 question in the negative, for at the critical stage of his 

 discussion he introduces arguments which are not physical, 

 but philosophical. 



Prof. Schuster asks, " Does it require explanation that 

 all star groups have the same velocity vector imposed upon 

 them?" Certainly; it requires explanation no more and 

 no less than any other distribution of velocities. It is 

 highly desirable that the equations of the proper motions 

 of the stars should be established and their past history 

 traced until the physical circumstance that determined 

 those motions is discovered. But this circumstance need 

 not be a body at absolute rest. In the analogy; which 

 Prof. Schuster gives, the inhabitant of a gaseous molecule 

 would be quite wrong if he decided that the rest of the 

 containing vessel was absolute. Accordingly, Prof. Schuster 

 has recourse to philosophical arguments. We have deter- 

 mined, he says, the velocity relative to a material body 

 which does not come within the range of our observations. 

 I should have thought that the mere fact that we had 

 determined a velocity relative to it proved that it had 

 come within the range of our observations ; the deduction 

 from the motion of some of the stars of the existence of 

 dark satellites near them seems an analogous case ; and 

 since, he continues, this conclusion is absurd, the body 

 must be replaced by something immaterial. Why is it less 

 absurd to determine a velocity relative to an unknown 

 immaterial than to an unknown material substance? 

 Finally, since the something is immaterial, it cannot be 

 in motion, and therefore it must be at absolute rest. The 

 term immaterial may have many meanings ; but I should 

 have thought that an immateriality which precluded a 

 substance from being in motion also precluded it from 

 being at rest. A thought, for example, is incapable of 

 motion, but it is equally incapable of rest; any application 

 to it of the terms motion or rest is not true or false, but 

 simply meaningless. 



It may also be pointed out that if the " something at 

 rest " is immaterial, the analogy breaks down. The dis- 

 tribution of the velocities of molecules in a gas depends on 

 the collisions with the walls ; but a star cannot collide 

 with an immaterial boundary. 



Prof. Schuster says that the attempt to make all motion 

 relative to the asther is inconsistent. With all respect, I 

 do not think he sees the point. The reasons for our 

 preference of the Copernican to the Ptolemaic hypothesis 

 are two-fold. The first reason is that the equations of 

 motion of the solar system are simpler on the former 

 theory. The second reason is precisely that which made 

 the theologians object to the Copernican hypothesis ; it 

 points out that it is the sun, and not the earth, which 

 holds a unique place in the solar system ; this is a question 

 of scientific taste. There are the same reasons for referring 

 all motions to axes fixed in the aether — if we could deter- 

 mine them. Firstly, an attempt is being made to reduce 

 all laws to electrodynamic laws, and these are simplest on 

 the basis of a fixed aether. Secondly, the aether holds such 

 a unique place in the physical universe that it is desirable 

 to direct attention to the fact. The question of the 

 " absolute motion of the aether " — if any — cannot come 

 within the range of physical discussion any more than the 

 " absolute motion of the sun " can come within the range 

 of any discussion based on the properties of the solar 

 system. 



* I should like to add a few remarks on the subject of 

 "absolute rotation." "Rotation." it seems to me, like 



