546 



NA TURE 



{Oct. 5, 



water, would the author thinks, be impossible were the 

 surface tensile. Doubtless, according to the author's 

 definition of tensile, it would be so, but we think it would 

 be equally impossible unless the surface were endowed 

 with a tolerably high tension, such as water is known to 

 possess. 



We find it impossible also to accept the author's ex- 

 planation of the various capillary phenomena on the 

 same hypothesis. To take the case of capillary elevation 

 and depression alone. If the surface force on a liquid 

 is extensile, it can be easily shown by reversing the 

 reasoning given in the ordinary physical text-books, that 

 in the case of capillary elevation, the free surface would 

 be convex, and in the case of capillary depression, con- 

 cave, conditions, precisely the opposite of those which 

 actually take place. The same hypothesis is equally un- 

 successful when applied to the resolution of jets into 

 drops. Mr. Stanley considers drops to be formed when 

 the mass cohesion of a jet is equal to the extensibility of 

 its surface, and in order to show that this is the principal 

 cause, he falls into the serious error of imagining that a 

 jet of liquid (water is the only one mentioned) issuing 

 from a small orifice, continually expands in sectional area 

 beyond the vena contracta, whether the stream be directed 

 upwards or downwards, the final resolution into drops 

 being due to such expansion caused by extensibility. 

 We know, however, that this cannot be the case, since 

 although the jet expands slightly beyond the vena con- 

 tracta, in accordance with the equation of continuity it 

 again contracts if flowing downwards, and the reverse if 

 flowing upwards, and since in either case, whether in 

 waterfalls or fountains, the jet ultimately becomes con- 

 verted into spray, the author's explanation is obviously 

 erroneous. It is to be regretted for many reasons that in 

 dealing with this interesting though difficult subject of 

 surface tension and capillarity of liquids Mr. Stanley 

 makes no mention of the researches of Van der Mens- 

 brugghe, Tomlinson, Duclaux, or of the very remarkable 

 results obtained not long ago by Cintolesi, and that 

 while the names of Young and Laplace are mentioned 

 once, not the smallest account is given of their researches 

 Chapter III. chiefly relates to the conditions of the 

 efflux of liquids through orifices. A great deal of it is 

 almost unintelligible from the obscurity of the language 

 employed, and the loose way in which the expressions, 

 energy, weight, velocity, force, and volume are employed 

 as though they were identical. 



As far as it is possible to glean anything definite from 

 such a chaos, it would seem that the author thinks the 

 known contraction which takes place in the area of efflux 

 of a liquid through a vent, is due to horizontal elastic 

 compressions caused by the reaction of the vessel against 

 the pressure of the liquid it contains. No reference is 

 made to the Torricellian equation, which according to the 

 author's notation should take the form v* = 4gh; instead 

 of igh as ordinarily ; or to the theoretical results got 

 with different forms of orifices on the parallel section 

 hypothesis. We do not think the author has got on the 

 right tack here. The horizontal velocities which must 

 necessarily arise, either from the natural or artificial 

 narrowing of the descending column, and which are dis- 

 regarded by the parallel section hypothesis, may be readily 

 conceived to act so as to contract the area of vertically 



descending liquid, and not elastic compressions, which 

 have little place in the dynamics of a practically incom- 

 pressible liquid. 



In Chapter IV. the author tries to show that the general 

 relative motion of fluids on solid surfaces or in other fluids 

 is effected by means of rolling contact. The hypothetical 

 case of a plane supported on equal rollers, and moving on 

 a parallel plane is taken, and the analogy to this pointed 

 out in different case;, such as where a river moving rela- 

 tively to its bank causes small lateral eddies, or where 

 larger rotatory movements are produced in the bays or 

 widenings through which it flows. Several instances 

 apparently exhibiting this kind of motion are noticed, but 

 we cannot agree with the author that such examples con- 

 clusively prove his theory, and that no sliding takes 

 place. The internal molecular friction or viscosity of 

 most liquids, must necessarily cause rolling contact, if it 

 occurs at all, to take place in a very imperfect manner, 

 and at the same time admit of sliding with a certain 

 amount of friction. 



In Chapter V., which treats of the resistance of fluids 

 to the projection of fluids or solids within them, Mr. 

 Stanley develops some novel nomenclature, and a prin- 

 ciple of considerable importance which may be briefly 

 enunciated as follows : — When a mass of matter strikes a 

 fluid such as water, it fractures a conical part imme- 

 diately in front of it, called the cone of impression, from 

 the surrounding mass called the conoid of persistion, and 

 intrudes itself into the fracture, which is called the plane 

 or cone of infraction. This principle, which is frequently 

 appealed to in subsequent portions of the work as one of 

 fundamental importance, and on which a host of minor 

 propositions depend, is derived from an analogous prin- 

 ciple of conic fracture in the case of solids, and is sup- 

 ported in the case of liquids and gases by various experi- 

 ments, such as the shape assumed by a leaden bullet shot 

 vertically into water, the ring formed by a drop of coloured 

 dropped into uncoloured water, and the phenomena of 

 smoke-rings as shown by Prof. Tait. The experiments 

 are clear, and the idea is skilfully and consistently worked 

 out as far as it goes. 



Whether all the properties of vortex-rings will be found 

 to accord with this principle, is a question which may be 

 safely left to those who make such matters their special 

 study, but at all events the explanation given of the sm oke 

 rings, and the experiments showing the absence of a 

 motive axis, are decidedly ingenious. 



From the foregoing principles the author proceeds to 

 deduce in Chapter VI. the conditions for the continuous 

 motion or projection of fluids within fluids, in which 

 rolling contact again comes into play, through the final 

 rotation of the conoid of persistion, and the formation of 

 whirl and biwhirl systems. Several interesting experi- 

 mental examples of such systems are described and 

 figured, and some of the laws which apparently regulate 

 such systems are proposed, though the proofs appear to 

 rest solely upon a somewhat limited ocular experience. 



Towards the end of this chapter is introduced the well- 

 known paradoxical fact first noticed by Clement De'sormes 

 and Hachette in 1826, that a blast of air or stream of 

 water flowing in their respective fluids, apparently attract 

 towards themselves flat bodies placed directly in their 

 paths, and an endeavour is made to account for it in a 



