NATURE 



549 



THURSDAY, OCTOBER 3, 1901. 



A SCIENTIFIC ENGINEER. 

 Papers on Mechanical and Physical Subjects. By Prof. 

 Osborne Reynolds, F.R.S. Vol. ii. 18 81-1900. Pp- 

 xit + 740. (London: C. J. Clay and Sons, 1901.) 

 Price 2 1 J. net. 



A FULL account of the first volume of Prof. Osborne 

 Reynolds' collected papers has already appeared 

 in these pages (vol. Ixii. p. 243). The second volume, 

 which is no less interesting than its predecessor, brings 

 the author's contributions to mechanical science up to 

 date and enables us to realise the value of the work he 

 has done. The twenty-seven papers here printed vary, 

 no doubt, in importance ; but throughout them all Prof. 

 Reynolds has kept one aim clearly in view, the applica- 

 tion of physical and mechanical principles to engineering 

 problems ; whether he is dealing, as in the first paper, 

 with the question of the fundamental limits of speed or, 

 as in the last, with the reasons why ice is slippery, this 

 aim is always before the author. 



It is difficult from a volume of this kind to make a 

 selection of points to notice ; there are, however, three 

 papers which stand out conspicuously as dealing in a 

 luminous manner with three fundamental problems. 

 The first is No. 44, an e.\perimental investigation of 

 the circumstances which determine whether the motion 

 of water shall be direct or sinuous, and of the law of re- 

 sistance in parallel channels. The second. No. 52, on 

 the theory of lubrication and its application to Mr. 

 Beauchamp Tower's experiments, and the third. No. 66, 

 on the method, appliances and limits of error in the direct 

 determination of the work expended in raising the tem- 

 perature of ice-cold water to that of water boiling under a 

 pressure of 29"899 inches of ice-cold mercury in Man- 

 chester. A few lines may be given to each of these in 

 turn. 



The fact that for narrow tubes and for small velocities 

 the resistance to the flow of water in a tube is propor- 

 tional to the velocity follows from the experiments of 

 Poiseuille and others. It was also known that this law 

 did not hold in larger tubes or when the velocity was 

 considerably increased, but the cause of the change and 

 the relation of the velocity to the radius for which it 

 occurred in a given tube were unknown until the date of 

 Prof. Reynolds' experiments. He showed that if D be 

 the diameter of the tube, V the velocity of the stream and 

 P the ratio of the coefficient of viscosity to the density, 

 then the change of resistance takes place at a velocity 

 V given by the equation \' = P BDwhen B is a constant, 

 and, moreover, that at this critical velocity the motion of 

 the water in the tube changes from direct to sinuous ; 

 eddies and vortices are set up which are intimately con- 

 nected with the change in resistance. Further experi- 

 ments showed that up to the critical velocity the slope of 

 pressure in the tube varies as the velocity, while for 

 velocities considerably greater than the critical the slope 

 of pressure varies as the velocity raised to the power of 

 172. 



The second paper deals with Mr. Tower's experiments 

 on lubrication. Mr. Tower had shown that when the 

 NO. 1666, VOL. 64] 



rubbing surfaces, the friction between which was being 

 investigated, were totally immersed in oil, a thin film of 

 oil was formed between them, within which the pressure 

 was enormously greater than in the oil bath ; in some 

 cases it was as much as 625 lbs. to the square inch above 

 the pressure in the bath. 



Prof Reynolds gives a very complete account of the 

 existence of this film and of the conditions for complete 

 and incomplete lubrication. 



In the last paper mentioned the author gives the 

 theory of a very valuable redetermination of Joule's 

 equivalent. 



The laboratory at the Owens College is fitted with a 

 set of triple expansion engines which can be arranged to 

 work on three special hydraulic brake dynamometers, 

 the energy being absorbed by a stream of water which 

 passes through the brake. This water can be taken 

 from a tank holding some 60 tons in a tower 116 feet 

 above the laboratory floor. 



The experiment, put briefly, consisted in measuring 

 the work put into the brake, the temperature of the in- 

 coming and outflowing water and the quantity of that 

 water. Prof. Reynolds' paper contains a detailed exposi- 

 tion of the theory, with an account of the precautions 

 taken and calculations required to allow for the various 

 sources of error. 



The experiments were conducted by Mr. Moorby, and 

 are very closely concordant. It results from them that 

 the mean specific heat of water between freezing and 

 boiling points is 776'94 ft. lbs., or in C.G.S. units 

 41832000 ergs. 



Other papers of great interest and importance might 

 easily be mentioned ; for these we must refer the reader 

 to the book itself, at the same time congratulating the 

 author on the conclusion of the task he was asked to 

 undertake and the Cambridge University Press on the 

 service it is rendering to science by its series of reprints 

 of mathematical and physical papers. 



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IN the preface to Dr. Holland's admirable " Butterfly 

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Enormous strides have been made in the study of 

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