136 REPORT— 1898. 



The above table gives the values in c.g.s. units of the Gaussian 

 magnetic constants, as determined by Adams for the epoch 1880, and by 

 Neumayer for 1885, by Schmidt for 1885, and by Fritsche for 1885. 

 The last two determinations by Schmidt and by Fritsche were derived 

 from the observations employed by Neumayer, and the values of the 

 Gaussian constants, corresponding to those published by Schmidt in the 

 first number of the journal ' Terrestrial Magnetism,' are obtained by 

 multiplying each magnetic constant by the value of the above factor 



^ for that constant. 



Stream-line Motion of a Viscous Film. 



« 



[Ordered by the General Committee to be printed in extenso.^ 



(I.) Experimental Investigation of the Motion of a Thin Film of 

 Viscous Fluid} By Professor H. S. Hele-Shaw, LL.D. 



At the International Congress of Naval Architects at the Imperial Insti- 

 tute in July of last year the author read a paper on the ' Nature of 

 Surface Resistance,' and thei'e showed by means of lantern experiments 

 that the flow of water round solids of various forms could be made visible 

 by injecting air into the flowing water. In response to an invitation from 

 the Institute of Naval Architects to read a second paper on the subject, 

 he endeavoured to investigate the nature of a very well defined border 

 line which existed in all the experiments when air was used, such as by 

 employing water under various conditions, injecting coloured fluid into 

 the flowing mass on the skin of the bodies in the path of flow. In 

 endeavouring to investigate the markedly diSerent condition of flow at 

 the surface, instead of using a thick sheet of water of from three-eighths 

 to half an inch, a thin sheet of water was employed the thickness of 

 which was not greater than that of the abovementioned Ijorder line. 

 The result of doing this was to reveal a different state of flow in the 

 water, in which, though the air method now failed, colour bands remained 

 stable and enabled the behaviour of the water to be clearly seen. 



The hypothesis had been advanced in the first paper that, while the 

 general body of the water in the thick sheet was moving with sinuous or 

 turbulent motion, the water near the skin (which of course corresponds 

 with that of the thin sheet) was in a state of parallel flow. The author, 

 by means of a formula which Professor Lamb was good enough to furnish 

 him with, found that within reasonable limits of error true stream line 

 flow took place under these conditions, and gave a number of illustrations 

 of this method of obtaining the form of stream lines round bodies of 

 various cross section and in channels of various forms. 



(1.) The Two Lines of Research possible by means of the Method of Thin Sheets. 



It is obvious that there are two lines of research for which this 

 method might be employed. The first of these is the investigation of the 

 properties of fluids by using sheets of difierent thicknesses and varying 



' The reproduction of the experimental results and diagrams which illustrated 

 the reading of this paper are given in Engineering and The Engineer. 



