68 



NATURE 



[March 17, 1910 



some years ago, and as the engines referred to were 

 designed many years before then, it is absurd to 

 illustrate them as modern practice when the magni- 

 ficent creations of Mr. Wilson Worsdell on the North- 

 Eastern and those of Mr. Mcintosh on the Caledonian 

 arc available. 



The compounding of locomotives has also been very 

 seriously considered by many engineers, particularly 

 during the last ten or twelve years. The Webb and 

 Worsdell systems being more or less obsolete, one 

 naturally expected to find the Smith system with 

 three cylinders, which originated on the North- 

 Eastern, engine No. 1619 being the prototype, de- 

 scribed and illustrated by one of the recent Midland 

 compounds. Another type of compound represented 

 by the four-cylinder engines on the North-Eastern is 

 conspicuous Sy its absence. 



Of the subject of superheat, which is now being 

 seriously considered by most locomotive engineers, we 

 find no reference in this volume. This is surely a 

 serious omission when there are locomotives running 

 on certain railways in this country fitted with the 

 Schmidt system, a system which claims many 

 economies in working when compared with the heavy 

 boiler expenses involved when working with the high 

 pressures necessary with the compound engine. 



Although we have considered it necessary to point 

 out that the author's claim of having brought the 

 third edition of this book up to date has more or less 

 failed, it should be clearly understood that its con- 

 tents are of a valuable nature, and budding locomo- 

 tive engineers should obtain a copy without delay. 

 It is certainly one of the best books of its kind. 

 The illustrations are good and the general style 

 excellent. 



Matter, Spirit, and the Cosmos. Some Suggestions 

 towards a Better Understanding of the Whence and 

 Why of their Existence. By H. Stanley Redgrove. 

 Pp. 124. (London : W. Rider and Son, Ltd., 1910.) 

 Price 2S. 6d. net. 

 Mr. Redgrove's theory of matter is that it possesses 

 only a hypothetical reality; we assume its existence 

 only because otherwise the harmony of our individual 

 worlds would be unintelligible. Spirit, he seems 

 to maintain, we know by direct intuition of ourselves 

 • — a proposition of great dubiety, if we take spirit in the 

 sense of real substance. But, granting the one a cer- 

 tain, the other a hypothetical objectivity, the objective 

 relation of the two must be determined. Mr. Redgrove 

 holds that God is the ultimate cause of both, spirit the 

 mediate cause of matter. Yet the effect must be re- 

 garded as quite distinct and discrete from the cause. 

 It would seem to follow that for God spirit is some- 

 thing analogous to what matter is to us ; but this infer- 

 ence is not drawn. Moreover, no reason is given for 

 the ontological subordination of matter to spirit, except 

 the epistemological distinction noticed above; and it 

 might equally be held to prove the ontological 

 subordination of all other spirits to one's own. 

 Mr. Redgrove, indeed, tentatively holds that in 

 telepathy we have direct "sense" of other 

 spirits ; but this perception is " symbolic " as well 

 as direct, which means, one must suppose, that it 

 is not truly immediate. The author believes in the 

 immortality of self-conscious beings ; but as he also 

 believes that self-consciousness arises out of proto- 

 plasmic consciousness by the ordinary processes of the 

 universe, it is not evident why he should assume the 

 Impossibility of a relapse into that state. Though 

 these and other diflficulties will be met, the book is 

 well worth reading. Mr. Redgrove writes with pre- 

 cision and force, and his discussion is always inter- 

 esting. 



NO. 2107, 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, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



The Colour of Water. 



I AM reminded by Lord Rayleigh's lecture on this sub- 

 ject of the splendid light-blue colour presented by the 

 tanks of water in which some of the water companies 

 allow the sedimentation to take place of " hard water " 

 which has been treated by Clark's process. I am think- 

 ing of those near Caterham and of those at Plumstead. 

 The tanks — to the best of my recollection — are about 

 20 feet by 40 feet in area and 15 feet deep. The water 

 in the tanks has become perfectly (or nearly) clear, whilst 

 the sides and bottom of the tanks are made brilliantly 

 white by the deposit of calcium carbonate. The intense 

 blue colour is seen at (practically) any angle of vision, 

 and on a sunless, overcast day as vjLvidly as in sunshine. 

 It would be important to ascertain'<|»hether the blue colour 

 thus seen is entirely due to the self-colour of the water 

 or whether the phenomenon is in any way due to the 

 minutest white particles of calcium carbonate which are 

 still floating in the apparently clear water, and are acting 

 as do the particles of a blue vapour-cloud. I suppose that 

 it would be an easy thing for a physicist to determine this 

 by the use of a polariscope at the side of the tank. 



Also the introduction of black tarpaulin into the tank 

 so as to prevent the reflection of light from the bottom 

 and sides would show whether any amount of blue colour 

 was still exhibited by the water, such colour being then 

 necessarily due to the reflection of light from suspended 

 particles, and not from the sides or bottom. A more satis- 

 factory method would be to draw off (without disturbing 

 the sediment) the blue-looking water into an adjacent tank 

 previously lined with dead-black. 



One observation on the colour of water I may venture 

 to record. In a very large porcelain (so-called) bath in a 

 hotel bath-room, where strong sunlight was admitted by 

 a window some 10 feet above the bath, the walls of the 

 room being colourless, I noticed that when the bath was 

 filled to a depth of 20 inches the water had a distinctly 

 blue colour. The porcelain, whilst pure white above, yet 

 beneath the water had a distinctly blue appearance, and 

 the intensity of the colour varied with the movement of 

 the water in waves or ripples. The colour was blue 

 rather than greenish-blue, and this I attributed to the 

 pure white of the porcelain as contrasted with the yellowish 

 tint of enamel. The water in question was that supplied 

 in the Hotel Ritz, in Paris (I think that of the Vanne). 



E. Ray Lankester. 



The Stability of an Aeroplane. 



I HAVE been much interested in reading Prof. Bryan's 

 statement on the subject of the stability of an aeroplane, 

 but I cannot agree with him in thinking that the solution 

 of the problem is to come from the mathematical side. 

 I should be the last to decry the use of mathematics irr 

 such a case, but if the final result is to be absolutely trust- 

 worthy, there must be no doubtful assumptions made 

 during the process. 



It does not appear, from the article written by Prof. 

 Bryan, whether he has taken the viscosity of the air into 

 account, but I presume that he has done so. Perhaps, 

 also, his solutions are only meant to apply to the case of 

 an aeroplane flying in a dead calm. The practical difficulty 

 with a flying machine is the natural wind, and if flying 

 machines are to be of any real use they must be able to 

 maintain their stability in ordinary conditions of weather. 

 Now it is obvious that when a flying machine has once 

 left the ground it is quite immaterial to the stability, pro- 

 vided the air motion is perfectly uniform and steady, 

 whether the velocity of the wind be one mile or one 

 hundred miles per hour, since it is only the relative motion 

 of the machine and the air with which we are concerned ; 

 but, as a matter of fact, a wind of from ten to twenty 

 miles an hour is fatal to almost every aeroplane, and the 



