270 SCIENCE IN SHORT CHAPTERS. 



this application of an old scientific plaything to useful purposes may 

 become of considerable utility, as it evidently opens a wide field for 

 further investigation and progressive improvement, by the applica- 

 tion of the enlarged powers which modern science places at the dis- 

 posal of ingenious inventors. "We hope, for the sake of all con- 

 cerned, that it will not fall into the hands of professional prospectus- 

 manufacturers and joint-stock-company-mongers, and that the story 

 of its triumphs will be told without any newspaper exaggerations. 



Since the above was written in February, 1880 I have tested this 

 luminous paint (Balmain's patent). Practically, I find it unsatisfac- 

 tory. In the first place, its endurance is far shorter than is stated. 

 It begins to fade almost immediately the light is withdrawn, and in 

 the coiirse of an hour or two it is, for all practical use though not 

 absolutely extinguished. Besides this it emits a very unpleasant 

 odor painfully resembling sewage and sulphuretted hydrogen. This 

 is doubtless due to the sulphur compound, but is, I have no doubt, 

 quite harmless in spite of its suggestions. 



CHAPTER XXXVIII. 



THE OEIGIN AND PEOBABLE DUEATION OF PETEOLEUM. 



IN spite of the enormous quantities of mineral oil that are continu- 

 ously drawn from the earth, and the many places from which it may 

 thus be drawn, geologists are still puzzled to account for it. If it 

 were commonly associated with coal the problem of its origin would 

 be solved at once. We should then be satisfied' that natural mineral 

 oil is produced in the same manner as the artificial product i.e. by 

 the heating and consequent distillation of certain kinds of coal or of 

 bituminous shales ; but, as a matter of fact, it is but rarely that petro- 

 leum is found in the midst of coal seams, though it is sometimes so 

 found. 



I visited, some years ago, a coal-mine in Shropshire, known as 

 "the tarry pit," thus named on account of the large quantity of 

 crude mineral oil of a rather coarse quality that exuded from the 

 strata pierced by the shaft. It ran down the sides of the shaft, filled 

 the " sumph" (i.e. the well at the bottom of the shaft in which the 

 water draining from the mine should accumulate for pumping), and 

 annoyed the colliers so seriously lhat they refused to work in the 

 mine unless the nuisance were abolished. It was abolished by " tub- 

 bing" the shaft with an oil-proof lining built round that part from 

 which the oil issued. The "tar," as the crude oil was called, was 

 then pumped out of the sumph, and formed a pool which has since 

 been filled up by the debris of the ordinary mine workings. 



A piiblican in the Black Country of South Staffordshire discovered 

 an issue of inflammable vapor in his dellar, collected it by thrusting 

 a pipe into the ground, and used it for lighting and warming pur- 

 poses, as well as an attraction to customers. 



These and other cases that might be cited, although exceptional, 

 are of some value in helping us to form a simple and rational theory 



