September 25, 1885.] 



SCIENCE. 



275 



In establishing his fundamental equations, Dr. 

 Whiting, like Van der Waals, treats the molecules 

 as elr^-stic spheres which attract one another when 

 not in contact. The cohesive effect of the molecular 

 attraction is regarded by both as proportional to the 

 square of the density. It is, in fact, represented by 



the same term f — i in equations (1) and (2). This 



6 



effect is deduced by Dr. Whiting from the hypothesis 

 of a molecular attraction varying inversely as the 

 fourth power of the distance, by supposing a body to 

 expand so that every distance is increased in the 

 same ratio ; but such an expansion is entirely unlike 

 any which actually occur in fluids, since it increases 

 the distance within which the centres of molecules 

 do not approach one another. We shall probably 

 come much nearer to the case of nature, if we sup- 

 pose that the average number of molecules in a fluid, 

 which are between the distances r and r + dr from a 

 given molecule, varies as the density of the fluid. 

 This supposition will evidently make the cohesive 

 effect of the molecular attraction vary as the square 

 of the density. It would seem that any agreement of 

 experiment with the indications either of equation 

 (1) or of equation (2) should be regarded as confirma- 

 tory of this law of the distribution of the molecules 

 rather than of any particular law of attraction. 



THURSTON'S FRICTION AND LOST 

 WORK. 



This volume combines characteristics not 

 too often found in a work on this or kindred 

 subjects. It is thoroughly scientific in method, 

 as v^-ell as in the treatment of separate problems. 

 It is eminently practical in results, as well as 

 in the selection and range of the problems con- 

 sidered. It is clear, accurate, and minute in 

 the details which give completeness to its dis- 

 cussions, and make them readily available for 

 actual use. It is not merel}^ or principally a 

 compilation. While it brings together the 

 formulae and results of the standard writers 

 and experimenters upon friction, its laws, 

 modifications, and effects, it also includes the 

 author's own elaborate experiments, made with 

 a view to their bearing upon questions of daily 

 and vital importance to the engineer and the 

 student. The conclusions drawn from these 

 experiments, being always subject to compari- 

 son with the facts and knowledge gained by 

 the author in a wide and extensive engineering 

 practice, are rational and reliable. The book 

 comprises eight chapters. The first explains 

 the object of mechanism, the manner of com- 

 puting work and power, the laws of the per- 



FHction and lont work in machinery and mill-work. By R. 

 H. Thurston. Xc-w York, Wiley, 1885. 12+365 p., illustr. 8°. 



sistence and transformation of energ}', and 

 the relation of lost work to the eflQciency of 

 mechanism. In the second chapter, the theoiy 

 and laws of friction are developed. The 

 problems which arise in practice are taken up 

 one by one, clearly analyzed, mathematical!}^ 

 solved, and the applications of the resulting 

 formulae pointed out. 



The next three chapters form an exhaustive 

 treatise on the lubricants used for reducing 

 friction; their nature and relative values; 

 the means of applying and using ; methods 

 of analyzing, inspecting, and testing them. 

 Cuts of the best lubricators in use, and also 

 of the apparatus used in making physical 

 tests ; tables giving physical and chemical 

 properties of oils, their color reactions, densit}', 

 specific gravit}", and viscosit}^ ; and diagrams 

 showing the relations of viscosity and lubri- 

 cation, and effects of temperature upon 

 viscosit}^ accompany the text. Oleograph}^ 

 and electrical conductivity are noticed as 

 methods of identifying various oils. The 

 nature and effects of friction, and the kinds 

 and properties of lubricants, having been thus 

 fully discussed, the author proceeds to the 

 subject of experiments, from which must be 

 obtained the values of constants which enter 

 into all the formulae. Upon the correctness of 

 these values depends the accuracy of results 

 obtained by calculation from the formulae 

 developed bj^ the theoretical investigations. 



The sixth chapter relates to experiments of 

 two kinds : First, those designed to ascertain 

 the relative amounts of friction between differ- 

 ent surfaces under varying conditions ; to deter- 

 mine constants, or suggest the value and form 

 of empirical formulae, appHcable to friction of 

 both solids and fluids. Second, experiments 

 with machines for testing lubricants, with cuts 

 and descriptions of oil-testing machines. The 

 mathematical theory and method of using 

 Thurston's machine are given in detail, to- 

 gether with tables showing records of oil-tests 

 made by the author with his machine. The 

 seventh chapter gives results of experiments 

 with lubricants, showing their effects in modi- 

 fying friction ; their endurance under different 

 conditions of pressure and A^elocit}' ; and the 

 effect of changes of pressure and velocity upon 

 the coefficient of friction. 



It is impossible to give in a brief review an 

 adequate idea of the minuteness of detail with 

 which the wide range of problems and experi- 

 ments are discussed. The reader may expect 

 to find, substantially, all that is known upon 

 these subjects through the investigations of 

 earlier writers, supplemented by the results of 



