juiy 2'/, 1888.] 



SCIENTIFIC NEWS. 



9 J 



the mineral world. They have extracted from the 

 primitive glassy mass the chemical elements of which 

 they consist, and which group themselves according to 

 their several affinities, just as we see, in a liquid satu- 

 rated with a solution of salt, crystals reforming the sub- 

 stance of which was previously dissolved in the mother 

 liquor. 



Mineralogy teaches us to define the different kinds of 

 minerals which crystallise in the lava, whilst chemical 

 analysis furnishes us with valuable information about 

 the composition of volcanic products. If we treat 

 eruptive rocks by a chemical process, we find that they 

 all contain a more or less considerable quantity of com- 

 bined silicate, which sometimes amounts to even 65 °/„ 

 of the whole mass ; these are acid or light lavas. Thence 

 we pass by various transitions to basaltic and heavy 

 lavas, in which the amount of silica, gradually diminish- 

 ing, does not attain to more than 55 % or 45 °/„. This 

 silica does not exist in a normal state in contemporary 

 lavas, but is combined in the form of silicates, with 

 aluminium, iron, lime, magnesium, potash, and soda. 



We find in the slag ol metallurgic industries products 

 which bear close analogies to those of volcanoes, both in 

 composition and formation. These artificial scoriae are, 

 like ihe lavas, formed of silicates, and a still stronger 

 similitude lies in the fact that the lava scoriae may be 

 considered as the dross of the internal metallic nucleus, 

 of which they form the upper layer. The differences 

 which we find in their compositions result from the 

 greater or less depths of the zones whence they are taken. 



Our knowledge of eruptive rocks has been increased 

 to an unlooked-for degree by the application of the 

 microscope to lithology. We have no space here to record 

 all the almost marvellous results obtained by this method 

 of investigation, inaugurated by H. C. Sorby, but, to put 

 it tersely, microscopical analysis has completely revo- 

 lutionised the study of stones. 



{To be continued.) 

 ♦-£»*^*^5«^ 



The New York State Entomological Station. — 

 The building erected at Cornell University consists of 

 two parts, a laboratory and a vivarium. The former in- 

 cludes a laboratory for the experimenter and his artist, a 

 laboratory for an assistant, a room for photographic work, 

 quarters for janitor, and a storeroom. The vivarium is 

 in the form of an ordinary botanical conservatory, sixty 

 feet in length, divided by a transverse partition into two 

 equal compartments. One of these is to be used as a 

 hothouse, the other is to be kept as nearly as possible 

 at the temperature of the aii outside. This vivarium is 

 to enable the experimenter to keep the insects that he 

 is studying alive upon growing plants where all the 

 conditions can be controlled. An arrangement has been 

 devised by means of which insects living upon roots of 

 plants can be observed continuously without disturbing 

 them. Another is to aid in the study of the relations 

 between ants and plant-lice. Others are for experiments 

 in the use of insecticides. — American Naturalist. 



Re-forestation in America. — Professor Willitts, of 

 the Agricultural College of Michigan, believes [Popular 

 Science Monthly) that the moisture on the American 

 continent is advancing westwards, and that the 

 planting of forests will cause the rainfall to spread year 

 by year further to the west. In Nebraska 700,000 acres 

 of forest have already been planted — the cotton-wood 

 and the willow first, and then the soft maple and the 

 hard woods. 



THE HEARING OF FISHES. 

 /"""AN fishes hear ? 



^ That is a question which must be variously 

 answered, according to the sense in which it is pro- 

 pounded. II it be asked whether they hear at all, we 

 must unhesitatingly reply in the affirmative. If informa- 

 tion be sought as to whether they hear as we do, our 

 decision may as unhesitatingly be given in the negative. 

 And, thirdly, if it be suggested that, while submerged in 

 the water, they can distinguish sounds in the air, we 

 must treat the proposition as one open to considerable 

 doubt. And to these three points let us now devote our 

 attention in turn. 



Do fishes, then, hear at all ? We may reply, as already 

 stated, without a moment's hesitation, that they do. For 

 in them we find the first rudiments of the auditory organs 

 which attain to such perfection in the higher vertebrates ; 

 and in many cases, to use a somewhat Hibernian ex- 

 pression, these rudiments are present in a fairly complete 

 state. And the very character of the organs of hearing 

 is such that, even in their most incipient stages, they 

 must necessarily be of more or less value to their owner. 

 One cannot imagine the work of evolution going on in 

 any sensory apparatus if the actual practical utility of 

 such apparatus were to be delayed until development 

 were complete. The organs, upon such a supposition, 

 would be of no possible value to their possessors while 

 still rudimentary, and so would have no chance of pre- 

 servation, still less of gradual development and perfec- 

 tion. And thus it seems evident enough that the mere 

 presence of an auditory system, however incomplete, 

 must imply that the sense of hearing is at least not 

 wholly wanting. 



It is true that fishes possess neither external ear, 

 Eustachian tube, nor tympanic cavity ; but that 

 affords us no proof whatever that they do not hear. 

 Water is so much more dense a medium than air that 

 its vibrations are and must be carried to the brain of any 

 animal submerged therein, whether that animal possess 

 ears or no. And the internal ear in the fish is so formed 

 that any such vibrations must be keenly felt and 

 appreciated, although of course not in the same degree as 

 in animals whose sensory apparatus is more perfectly 

 developed. 



But in no aquatic creatures do we find the external 

 ears of any great dimensions. In the whales and the 

 seals those organs are almost microscopical, in propor- 

 tion to the bulk of the body. In certain semi-amphi- 

 bious animals (I use the adjective in its popular sense) 

 they are so formed that they close instantly upon sub- 

 mergence, and remain practically non-existent until the 

 head is raised from the water. And the reason is 

 evident enough. Water, as a denser medium, transmits 

 vibrations with so much greater intensity than air that a 

 submerged animal possessing ears adapted for the recep- 

 tion of atmospheric sound would be literally stunned by 

 such a shock as that resulting from a heavy blow upon 

 the surface. The North American Indian, walking over 

 a frozen river in mid-winter, sees a beaver swimming 

 below him, and immediately brings down his club with 

 all his force upon the ice. The shock is borne to the 

 water, and through the water to the brain of the beaver, 

 which, stunned by the concussion, is drawn out through 

 a hole hastily cut in the ice before it recovers its senses. 

 Were a whale gifted with ears corresponding in size to 

 its bodily dimensions it would probably be killed by the 

 shock resulting from the first blow of its own tail upon 



