48 



KNOWLEDGE. 



[March 1 , 1898. 



ii/nis fatuus. Takiag advantage, apparently, of Priestley's 

 discoveries — for, as he appropriately remarks, it was im- 

 possible to explain the iijnis fatuus before gases were 

 discovered — he proceeds to describe the following capital 

 experiment, which we must let him relate in his own 

 language : — 



" II est bieu prouve, par I'experience et robserration, que dans les 

 marais, et les terrains marecageux, il y a de Fair inflammable ; il 

 sufEt, pour en obtenir, de remuer avec une canne la vase de ces 

 endroits, aussitot on Terra s'en ecbapper, a travers de I'eau qui en 

 courre plus ou moins U surface, une qumtite assez considerable. Si 

 dans cet instant on approehe la lumi^re d'une bougie on Terra aussit6t 

 I'air inflammable s'alhimer, et la flamme s'etendre au loin." 



Ths gas thus formed has been c Dllected in bottles full 

 of water inverted in the water of the marsh with a funnel 

 in the neck of the bottle. Ou stirring the mud below, the 

 gas enters the funnel in bubbles, and, rising up, displaces 

 the water in the bottle. It was found by Sir Humphry 

 Davy and others to contain carbonic acid and a small 

 quantity of nitrogen, the proportion of either or both of 

 which would, of course, iafluence the character of the 

 flame. Davy found the pure gas to consist of four parts 

 of hydrogen in chemical union with one part of carbon, 

 identical in composition with the fire-damp of the coal 

 mine. It is known as marsh-gas, or light carburetted 

 hydrogen. It is the only source of the ignis fatuus, properly 

 so called. It is ignited either by lightning or by an 

 accidental flame. I knew it in one case to be ignited by a 

 labourer passing by a marsh lighting his pipe and throwing 

 the match away. Another case has recently come under 

 my notice. An old pupil of mine informed me that four 

 or five years ago he was rowing in a boat with some 

 friends ou a pool of some three acres in extent. A stream 

 of water flowed through it, but the pool was stagnant, or 

 nearly so, in the rear of an island in the pool. At this 

 spot he noticed large bubbles of gas rising and bursting, 

 and at once surmised that they contained marsh-gas. To 

 test this he applied a lighted match, but not taking heed 

 as to the direction of the wind, the flame from a large 

 bubble instead of being blown away from him was blown 

 towards him, and burnt all the hair from oS' the back of 

 his hand. Many trees grew near the spot, and leaves fell 

 abundantly into the water, so that in the course of years 

 the decaying matter had produced a considerable deposit 

 of mud, which necessitated the emptying and cleansing of 

 the pool, after which the production of marsh-gas ceased. 



The ii/iiis fatuus is now seldom or never seen, and the 

 reason is that the places which produced it have been 

 drained and brought under cultivation. Some years ago, 

 however. Major Blesson of Berlin made a number of 

 capital experiments on the subject in a valley in the forest 

 of Gubitz, in the Neumarck, where the meteor had been 

 often seen. The valley cuts deeply into compact loam, and 

 is marshy at its lower part. The water of the marsh 

 contains iron, and is covered with a shining crust. During 

 the day bubbles of gas were seen rising from it, and at 

 night bluish-purple flames were observed playing over the 

 surface. On visiting the spot by night, the sensitive 

 flames retired as the major advanced ; but on standing 

 quite still, they returned, and he tried to light a piece of 

 paper at them, but the current of air produced by his 

 breath kept them at too great a distance. On turning 

 away his head, and screening his breath, he succeeded in 

 setting fire to the paper. He was also able to extinguish 

 the flame by driving it before him to a part of the ground 

 where no gas was produced ; then applying a flame to the 

 place whence the gas bubbles issued, a kind of explosion 

 was heard over eight or nine square feet of the marsh ; a 

 red light was seen, which faded to a blue flame about three 

 feet high, and this continued to burn with an unsteady 



motion. As the morning dawned the flames became pale, 

 and seemed to approach nearer and nearer to the earth, 

 until at last they faded fi-om sight. The same observer 

 also made experiments in other places. At Malapane, in 

 Upper Silesia, he passed several nights in a forest where 

 the meteor was to be seen. In the Komski forest, in 

 Poland, the flame appeared of a darker hue than usual, 

 and on attempting to ignite paper and shavings of wood 

 t'ley became covered with a viscous kind of moisture, as 

 ia Musschenbroek's observation, when an iiinis fatuus was 

 '• catched." On another occasion he succeeded in lighting 

 up the meteor by standing at a distance and hurling 

 ignited fireworks into the marshy ground. He visited by 

 night the summit of the Porte Westphalia, near Minden ; 

 the meteor was not visible, but on firing a rocket into the 

 marsh a number of small red flames were observed, which 

 soon went out, but appeared again on firing another 

 rocket. 



Hence, it will be seen that the if/nis fatuus, or " will-o'- 

 the-wisp" or "jack-o'-lantern," is due to the ignition of 

 a gas arising from the decay of vegetable matter, and 

 known as marsh-gas, or light carburetted hydrogen. 

 Low-lying meteors due to phosphorus and electricity 

 will be treated of in another article. 



Hettfrs. 



[The Editor does not hold himaelf responsible for the opinions or 

 statements of correspondents.] 



To the Editor of Knowledge. 



Deae Sir, — May I suggest to the writer of " The 

 Astronomy of Shakspeare " in Knowledge, that the seven 

 stars referred to when Falstaff says, " Indeed, you come 

 near me now, Hal : for we that take purses, go by the 

 moon and seven stars, and not by Phoebus," are the seven 

 stars forming Charles' "Wain? — for this constellation, after 

 the moon, forms the most conspicuous object of the night 

 sky. Believe me, yours sincerely, 



Harold M. Collison. 



Hillsboro', Wallington, February 2nd, 1893. 



[Mr. Collison is probably right, for in Shakspeare's time 

 it was necessary to count in the sun and moon to make up 

 the seven planets. FalstaS' probably did not refer to the 

 seven stars of the Pleiades, but to the better known seven 

 conspicuous stars of the Great Bear, which pointed out 

 the north and indicated the time to the intelligent 

 traveller. A friend reminds me that the Latin and 

 French word for north, septentrionale, is derived from these 

 seven stars, and that the Great Bear is still commonly 

 referred to in Italy as the seven stars. — A. C. Ranyard.] 



THEORY OF THE SUN. 

 To the Editor of Knowledge. 



Sir, — I hope you will allow me to answer briefly the 

 objections enumerated in the last number of your magazine 

 against my explanation of the prominences as merclij 

 eranescent illuminations caused bii the prnpaijation of chemical 

 action in compiratively tranquil matter 



Miss Gierke states " that the rate of propagation of 

 chemical action is, so far as terrestrial experience goes, 

 exceedingly slow as compared with the enormous velocities 

 testified to by line-displacements in prominences." That 

 objection would bo fatal if even the least analogy could be 

 expected between the propagation of chemical action in the 

 hot solar atmosphere and such a propagation in the ignited 



