'i48 



SCIENCE. 



[Vol. I., No. 9. 



LETTERS TO THE EDITOR. 

 Cracking in ice. 



1 NOTICED recently a peculiar cracking in ice. 

 Snow liad fallen to the depth of abont a foot, and 

 Lad been followed by a cold rain ; so that the snow 

 was covei-ed with a layer of ice about three-quarters 

 of an inch thick. The snow immediately under the 

 ice was more firmly packed than that farther down; 

 so that pieces broken ottt had their under-surfaces 

 covered to a depth of about three inches with close- 

 ly-packed snow. 



The cracks seemed to run over the field irregularly, 

 ■without legard to the conformation of tlie surface. 

 In one or two cases they seemed to have a 'radiant' 

 point in a bunch of thistles. Their peculiarity was 

 an the fact, that, for a great part of their extent, tliey 

 Avere almost j^erfect sinusoid cuiwes. Where a crack 

 'began, or joined another, it would run quite straight 

 for ten or twelve feet; and then the curves would 

 ^commence. Most of the curves were of the same 

 sine, — about three feet and a half from crest to crest. 

 The two edges of the ice where the crack was were 

 separated about a quarter of an incli to half an inch, 

 and one was uniformly a little higher than the other. 



Jacob Reighapd. 

 L:i Porto, Ind., Feb. 10. 



Caterpillars eaten by a kitten. 



One of our beatitiful springs was sadly rifled of 

 'Ijeauty and comfort by severe inroads of insects. 

 Elms of noble promise hung around my lawns chiefly 

 as chandeliers for the constant descent of canker- 

 worms. Following the gardener, a pet kitten was 

 attracted by this novel harvest. She ate the cater- 

 pillars with infinite relisli; and so long as canker- 

 worms hung from the trees, so long did the kitten 

 pass her time in constant leaping after the pendant 

 worms. Among my birds, only my little Black-cap 

 was her rival in rapid voracity. Fed by them as 

 gatliered in bowls, the mocking-bird was not to be 

 named in comparison with either. M. C. Sparks. 



Badly crystallized -wrought iron. 

 This seems to be such a condition of affairs as is 

 pointed out by Mr. Kirkaldy, who shows that a 

 crystalline fracture is not an indication of the 

 strength of material, but simply of the way in which 

 ruptui'e is effected. A smlden fracture always shows 

 crystalline constitution. In the broken walking-beam 

 referred to by Mr. T. M. Clark (p.lOQ), the exterior lay- 

 <!rs doubtless yielded gradually, and the Interior layers 

 suddenly; which accounts for the crystalline appear- 

 jince in tlie latter case, and the fibrous appearance 

 in the former. I think similar cases will be found 

 reported in Mr. Kirkaldy's excellent work. C. S. 



Eadiant heat, and the second lavsr of thermo- 

 dynamics. 



The application made by Prof. J. W. Gibbs of the 

 <loctrine of radiation (Science, p. 100) would seem 

 to me in all points to be coriect, were it not really a 

 question of the composition of velocities, of which no 

 sufficient account seems to be taken. 



To make this clear, suppose a body (such, for exam- 

 ple, as a right cylinder) to be projected lengthwise in 

 empty space of uniform temperature, with a velocity 

 equal to that of radiant heat. No heat can then over- 

 take its rear surface: hence its front will receive a 

 double amount, and so have Its temperature aug- 

 mented; thus causing he,it to flow along the cylinder 

 from front to rear. But any disturbance of tempera- 

 tures, such as this, is in apparent contradiction to 



the proposed application of the doctrine of radia- 

 tions, which attempts to prove in general that no 

 changes of temperature can arise from the motions of 

 bodies. It is not quite certain that this would also 

 constitute an exception to the second law, although 

 it may well do so, because the radiations encountered ■ 

 may possibly cause a pressure upon the front surface; 

 though it is difficult to see how this can be so in case 

 it is entirely black. This illustration, then, which 

 needs more complete discussion, will at least serve to 

 make evident the necessity of taking Into account the 

 velocities of moving bodies in cases in which no such 

 pressures oppose their motion. This is what has been 

 attemjited in the brief computation contained in the 

 original paper; ' and it seems to be admitted, in so far 

 as direct exchanges of radiant heat between A and B 

 are concerned, that more is transmitted in one direc- 

 tion along a line of apertures, a c b, than in the other. 



Now, suppose tlie screens to be non-conducting, 

 and enclosed by a non-conducting cylindrical surface; 

 also let the entire interior of the cylinder and screens 

 be perfectly reflecting. Then no part of the interior 

 can be a continuous source of radiant heat. The en- 

 closed space is also excluded from exchanges with all 

 bodies except A and B, and these only exchange heat 

 through apertures in the screens. 



It appears possible, by suitable reflectors moving 

 with the screens, to return to A and B respectively all 

 heat radiated from each which does not pass through 

 the screen c. Now, if a less amount of heat pass in 

 one direction through the apertures a c b than in the 

 other, then. In order that equilibrium may continue, 

 more heat must pass through c along other lines. But, 

 as there are no sources of heat in the interior, tills can- 

 not continue, although true at the start. It is there- 

 fore sufficient, in attempting to establish the proposed 

 process as an exception to the second law, to show, 

 as has been attempted, that more heat is transmitted 

 directly from A to B than from B to A; since their 

 exchanges with other bodies and parts of the appa- 

 ratus may be left out of the account, as was tacitly 

 assumed in the original paper. H. T. Eddt. 



Keiweena-w-point geology. 



On account of certain statements in Prof. K. D. 

 Irving' s letter in Science, March t), it seems proper 

 to attempt to undeceive him regarding the position 

 of some geologists towards the evidence of the Wis- 

 consin survey, and to make clearer to others the 

 points of discussion. That evidence has neither 

 been ignored nor denied by them; but, while willing 

 to grant its correctness, they deny the conclusions 

 that Irving and his associates have drawn therefrom. 

 Foster and Whitney, in 18.50, clearly showed that 

 the copper-bearing traps were a series of lava-flows, 

 between which, in many places, were conglomerate 

 and sandstone beds, composed, in part, of the debris 

 of the nuderlylug lava. These detrital deposits were 

 laid down on one lava-flow, and then the succeeding 

 flow was poured over all. Later, Mr. A. R. Marvine 

 brought forward full evidence of the same kind. 

 The "present writer also collected similar proof, and, 

 in addition, showed that the traps overflowed and 

 indurated the eastern sandstone. 



The structure of the district along a line extend- 

 ing obliquely from Torch Lake to Copper Falls, across 

 the eastern trappeau belt, and uniting the sandstone 

 on both sides, is .as follows: On the eastern side of 

 Keweenaw Point a series of sandstone and conglom- 

 erate beds was laid down, having a gentle but in- 

 creasing dip as the tr.aps are approached; over these 

 pouredthe first lava-flow, indurating the underlying 

 ' Journ. Franlil. Inat., March. 



