Mr. C. Tomlinson on the Ignis Fatuus. 465 



been honorary examiner in Physics to the Birkbeck Institu- 

 tion during many years, and can bear ample testimony to the 

 excellence of its scientific teaching. 



There is, however, a good deal of indifference in private 

 life as to whether science is taught or not, or how r it is taught. 

 In some cases this indifference is based upon ignorance of the 

 importance of such knowledge ; in other cases there is a 

 decided prejudice against it, because it is supposed to conflict 

 with certain theological dogmas. 



Even when such prejudices are absent, there is a want of 

 discrimination in the selection of text-books for the young, 

 and it is often a mere chance if a book written by a competent 

 hand is selected. 



I was led into these reflections by a passage that was 

 recently submitted to me from a book on Popular Science 

 which has passed through many editions. It professes to 

 give an account of the Ignis Fatuus. 



" This luminous appearance (which haunts meadows, bogs, 

 and marshes) arises from gas of putrefying animal and 

 vegetable substances, especially from decaying fish. These 

 luminous phantoms are so seldom seen because phosphoric 

 hydrogen is so very volatile that it generally escapes into the 

 air in a thinly diffused state. They fly from us when we run 

 to meet it, because we produce a current of air in front of 

 ourselves (when we run towards the ignis fatuus) which drives 

 the light gas forwards. It runs after us when we flee from 

 it, because we produce a current of air in the way we run, 

 which attracts the light gas in the same course, drawing it 

 after us as we run away from it. The Welsh ' corpse candles ' 

 are the same thing as the ignis fatuus. Swarms of luminous 

 insects passing over a meadow sometimes produce an appear- 

 ance similar to the ignis fatuus." 



It is impossible to suppose that this account was written 

 by a scientific chemist ; it was probably the work of one of 

 those gentlemen in the Reading-Room of the British Museum 

 who disturbed Mr. Carlyle in his studies : — " The use they 

 make of the Library/'' he said, " is to assist them in drawing 

 up articles for Compilation, Dictionaries, and Encyclopaedias, 

 and the stuff called ' Useful Knowledge/ They are a very 

 thick-skinned race." * 



The gentlemen thus referred to are often greatly indebted 

 to the Cyclopaedias in getting up books of Popular Science. 

 But though the Cyclopaedias themselves have been greatly 



* Evidence ' before the Commissioners appointed to inquire into the 

 Constitution and Management of the British Museum, 1849. 



Phil, Mag. S. 5. Vol. 32. No. 198. Nov. 1891. 2 I 



