490 Transactions. — Cliemistry. 



numerous cases wliicli are analogous to the present one, that I need not do 

 more than point out to you the fact that such a kind of application would 

 then be both right and necessary to make. 



Art. LXXXIII. — On the Nature and Cause of Tomlinson'' s Cohesion Figures. 



By William Skey. 

 [Read before the Wellington Philosophical Society, 9th Noveviber, 1878.] 

 It has long since been known that when any oil is suffered to flow on water 

 in very thin films a beautiful play of colours is produced ; but it was not 

 till the year 1868 that it was observed certain figures were at the same time 

 formed at a rate and of a pattern varying according to the kind of oil used. 



These figures are made up of small annular spaces, set in a ground of a 

 different shade, and are known as Tomlinson's cohesion figures, after Prof. 

 Tomlinson, the discoverer of them. They are employed by Dr. Moffat, 

 lecturer on chemistry, at Glasgow, to base thereon a system of olegraphy 

 (that is, one by which oil may be identified), and it is their precise nature 

 and more immediate cause which I now wish to discuss before you, as I 

 have been led by recent investigations of mine upon oils, to believe that 

 neither the one nor the other have been heretofore in the least apprehended, 

 and this, because the possibility of chemical reactions being involved in the 

 production of these figures has not been contemplated. 



Thus, as far as I can gather from the statements of Prof. Tomlinson 

 and Dr. Moffat (the only scientists who have, within my knowledge, inves- 

 tigated this subject), the annular spaces are "perforations" or "holes," 

 bottoming, as it necessarily follows, upon the water-surface used, and set in 

 a ground which is presumedly formed of oil. Now I think the annexed 

 account of observations made by me, will show to you very clearly that all 

 this is directly opposed to the facts of the case. 



First, then, in regard to the annular spaces (the so-termed " perfora- 

 tions" or "holes"). A careful inspection of them showed me that the 

 surface in these parts is not at all depressed as compared with that of the 

 rest of the patterns, but is, on the contrary, raised, either in flat or round- 

 topped hills according as these spaces are of large or small extent. I 

 further found that the liquid occupying these parts — that is, the hills — 

 burns completely away, and without the least splattering, showing that it 

 is an oiL 



