265 



NATURE 



{jfiily 2 2, 1880 



The dangers of an explosion of gas, such as that wliich 

 occurred on the evenins; of the 5th inst. in Bedford Street, are 

 not it would seem, limited to the immediate vicinity of the 

 accident. 



At about 7 p.m. on that day I was reading in a room, wliich 

 from its position at the baclc of the home being rather dark, 

 required a light, when I was startled by a sudden rush of the 

 flame from the single gas-burner upwards for about two feet— it 

 immediately subsided, again blazed up, and repeating this a third 

 time sank, and went out altogether. 



I thought something had gone wrong in the pipe, and that the 

 passage of the gai was interrupted, but on applying a match it 

 ignited and burned naturally, though with a feebler flame than 

 before. 



It was fortunate that I wa? in the room to turn oflf the escaping 

 gas, or some serious mischief might have occurred when next 

 any one had entered the room to find gas and air mingled into 

 an explosive compound. I fouid that two other gaslights in 

 passages had been extinguished at the same time, attention 

 having been called to them by the smell of escaping gas. 



As the distance of my residence — Granville Place, Portman 

 Square — is more than a mile from the site of the explosion, it is 

 interesting to note the distance to which the impulse extended. 



As no further disturbance occurred, and as the phenomena 

 noted happened synchronously or nearly so with the explosion, 

 and as the gas-pipes here are, I believe, branches of the same 

 source of supply, I assume that what I observed and have 

 described was in s^me way caused by the explosion. 



Fortunately it was at an hour when the gas was not generally 

 burning, or other accidents might have resulted. It would be 

 interesting to know if others observed similar effects of the 

 explosion. J. Fayrer 



July 10 



The Tay Bridge 



There are two interesting scientific questions, apart from 

 engineering proper, which are suggested by the late inquiry, 

 although no reference seems to have been made to them in the 

 reports. 



The first is the origin of the extraordinary flash seen at the 

 moment of the downfall of the bridge by many spectators several 

 miles away. It is scarcely doubtful that an impact was the 

 only possible cause. 



The second is the important question of the amount of wind- 

 pressure which would suffice to force a train bodily olT from the 

 top of the bridge at a place where it was not linthin the girder. 

 No strength of columns could then prevent an accident. 



The flash seems to prove that the train had been blown off 

 the rails, and had come into violent contact with the sides of 

 the high girders. Then, and not sooner, the piers were subjected 

 to a strain they were unable to bear. G. II. 



" Geology of the Henry Mountains " 



I LATELY received, through the Home Office at Washington, a 

 " Report on the Geology of the Henry Mountains," by G. K. 

 Gilbert, being a portion of the "Geography and Geology of the 

 Kocky Mountains." With the merits or demerits of this paper I 

 am not concerned. I am not prepared, how ever, to pass in silence 

 and without prote.-t the following paragraphs, which I find at 

 p. 76 : — " Eischof attempted, by melting eruptive rocks in clay 

 crucibles, to obtain their ratios of expansion and contraction, but 

 his method involved so many sources of error that his results have 

 been generally distrusted. He concluded that the contraction, in 

 passing from the molten to the crystalline state, is greater in 

 acidic than in basic rocks. Delesse, by an extended series of 

 experiments in which crystalline rocks were melted and after- 

 wards cooled to glasses, showed that acidic rocks Incre.ise in 

 volume from 9 to 11 per cent, in passing from the crystJIin; 

 state to the vitreous, while basic increase cnly 6 to 9 per cent. 

 JIallet concluded, from some experiments of his own, that the 

 contraction of rocks in cooling from the molten condition is 

 never more than 6 per cent., and that it is greater with basic 

 than with acidic rocks ; but considering that the substances 

 which he treated were artificial and not natural products, that 

 his methods were not uniform, and that he ignored the distinc- 

 tion between the vitreous and the crystalline, of which Delesse 

 had demonstrated the importance, no weight can be given to 

 his results." 



It would be difficult to compress into the same number of 

 lines a greater amount of eiToneous statement than is to be found 

 in the above quotation. Bischof's results were never distrusted 

 by geologists, by whom they were repeatedly quoted, until in 

 my paper on the "Nature and Origin of Volcanic Energy," read 

 to the Royal Society, June, 1S72, and printed in P/nl. Trans., I 

 pointed out the errors incidental to Bischof's method of experi- 

 ment, and at the same time directed attention to the strange 

 arithmetical blunder of Bischof himself, by which his deductions 

 from his own experiments are rendered still wider from the truth. 



The experiments of Delesse, which I presume are referred to, 

 w ere made on so small a scale that no deduction as to the total 

 contraction between the liquid and solid state of any rock can be 

 inferred from them. Coming now to Mr. Gilbert's summary 

 condemnation of my own experiments on the total contraction 

 of basic slags from the iron-smelting furnaces of Barrow (Cum- 

 berland), an account of which is given in my paper already 

 referred to, and printed in the Phil, Trans, for 1873, some of 

 the chief results of which are to be found in p. 201, I have to 

 remark that no other experiments on the subject, conducted on 

 the same great scale, and with equal precautions to insure exact- 

 ness, have ever been made and published. No experiments have 

 ever been made upon the contraction of lava as flowing from a 

 volcano and its solidification on cooling, but I have given 

 comparative analyses of natural lavas, and showm their almost 

 identical composition with that of the slags employed by me. It 

 is incorrect to state that I have ignored the difference between the 

 vitreous and crystalline condition ; all the melted matter experi- 

 mented on by me having, from the large bulk of melted matter, 

 cooled in the crystalline state. Whether then any justification 

 can be adduced for Mr. Gilbert's sweeping and unsupported 

 statement that "no weight can be given" to the results of my 

 experiments I leave to the judgment of men of science who have 

 impartially read my results. Robert Mallet 



London, July 7 



Intellect in Brutes 



The Central Prison at Agra is the roosting-place of great 

 numbers of the common blue pigeon ; they fly out to the neigh- 

 bouring country for food every morning, and return in the evening, 

 when they drink at a tank just outside the prison walls. In this 

 tank are a large number of freshwater turtles, which lie in wait for 

 the pigeons, just under the surface of the water and at the edge of 

 it. Any bird alighting to drink near one of these turtles has a 

 good chance of having its head bitten off and eaten ; and the 

 headless bodies of pigeons have been picked up near the water, 

 showing the fate which has sometimes befallen the birds. The 

 pigeons, however, are aware of the danger, and have hit on the 

 following plan to escape it. A pigeon comes in from its 'long 

 flight, and, as it nears the tank, instead of flying down at once 

 to the water's edge, will cross the tank at about twenty feet above 

 its surface, and then fly back to the side from which it came, 

 apparently selecting for alighting a safe spot which it had re- 

 marked as it flew over the bank ; but even when such a spot has 

 been selected the bird will not ahght at the edge of the water, 

 but on the bank about a yard from the water, ami will then run 

 down quickly to the water, take t«o or three hurried gulps of it, 

 and then fly off to repeat the same process at another part of the 

 tank till its thirst is satisfied. I had often watched the birds 

 doing this, and could not account for their strange mode of 

 drinking till told by my friend, the superintendent of the prison, 

 of the turtles which lay in ambush for the pigeons. 



The same friend had a couple of Hill Mynahs (Gracula 

 rdigiosa] the most wonderful bird for mimicry which I have 

 come across, not excepting the grey parrot of the West African 

 coast. One of these birds, when hung out in the verandah 

 during the afternoons, used to amuse itself by calling the fowls 

 together, imitating the call of their keeper so well that they 

 us 1 to flock together under the cage, when the bird would 

 tju St oi into a very good imitation of a human laugh, as if it 

 qiieenj ye.l the fun of taking in the fowls. Have birds the 

 sense of amu ement? This one certainly seemed to derive grati- 

 fication from the way in which it had cheated the fowls. 



Roorkee, June 21 W. W. Nicholls 



The Volcanic Dust from Dominica 

 Some months ago, through the kindness of Messrs. Alexander 

 Agassiz and S. II. Garman, some of the volcanic ashes which 

 fell in Dominica on January 4 were placed at my disposal. On 



