88 



SCIENCE. 



Vol. XXII. No. SSQ 



of other planets, and if there had ever been any differ- 

 ence, which is unlikely, considering the general unity of 

 the solar system, it must long ago have disappeared in con- 

 sequence of this interchange. 



The argument is strengthened by what we know of the 

 atmospheres of the planets, esjDecially of our nearest 

 neighbors. Mars and Venus. Not only do these planets 

 give plain indications of their atmosjaheres, but it is cer- 

 tain that they are very much like our own. That is found 

 out in the following way: Amongst the many dark lines, 

 Fraunhof er lines, as they are called, in the solar spectrum 

 there are certain well marked groups which Sir D. Brew- 

 ster long ago pointed out to be due to the absorption of 

 rays hj our atmosiDhere, because they are seen to be 

 blacker and more intense when the sun is low than when 

 he is high in the sky. That is because the rays have to 

 pass through a greater thickness of air before they reach 

 us when the sun is nearer the horizon. Now, by carefully 

 observing the light reflected from Yenus and Mars, which 

 must have twice passed through so much of their atmos- 

 pheres as lies above the reflecting surface, it has been 

 found that precisely the same rays which are darker when 

 the sun is low are also darker in the spectra of these 

 planets. Moreover, in these jslanets there are no new dark 

 lines indicating any absorbent of a different kind. The 

 more distant planets show additional absorption bauds, 

 but their atmosj^heres must, on account of theii^ greater 

 masses, perhajjs also from lower temperature, be denser, 

 and besides they apj)ear to be full of clouds which may 

 not be merely water-dust, and may well produce their 

 own absorptive elfects. 



The argument, however, reaches a good deal farther. 

 Not only are the planets moving through the so-called 

 planetary sjjace, but the sun and all its train are moving 

 through the interstellar space. Astronomers are agreed 

 that we are moving, but the direction of the movement is 

 much better known than the pace. The rate is sometimes 

 set down at about thirty miles a second: certainly not an 

 extravagant estimate. But at any rate we are going, and 

 leaving the interplanetary atmosphere, or some of it, behind. 

 Even if the solar system had no such motion, the process 

 of diffusion must gradually carry the interplanetary at- 

 mosphere into regions beyond, and, unless this diffusion 

 were compensated hj accession of air from without, the 

 planets must gradually lose their atmospheres until the 

 loss was stojjped by the cooling effect before mentioned. 

 After countless ages we have manifestly not reached that 

 stage, so we must conclude that interstellar space is per- 

 vaded by an atmosphere, though it be of very great 

 tenviity. 



If this atmosphere is not of similar chemical constitu- 

 tion to our own, ours must be changing by slow degrees, 

 and in course of ages the change must tell. There is, 

 however, no reason to think that our atmosphere has for 

 millions of years undergone any change sufficient to affect 

 the constitution of animal life of the higher types, and if 

 that be so the air of stellar space must be much the same 

 as that of interplanetary space and our own. Sterry Hunt, 

 from the jDreiJonderance of vegetable growth at certain 

 periods of the earth's history, inferred that at those jDeri- 

 ods there must have been an excessive quantity of car- 

 bonic acid in the atmosphere; and he fancied that this 

 was acquired from the stellar space as the solar system 

 made its way into regions where there was an unusual 

 amount of carbonic acid. Spectrum analysis has not led 

 us to think that the chemical elements of the stars of any 

 region are different from those with which we are ac- 

 quainted in the earth and in the sun. Stars in the same 

 region are mostly of the same type, and the types are few, 

 and all the common types of spectra of stars give indica- 

 tions of elements which we know, and no certainty of any 



other elements. Distance makes no difference at all. The 

 few stars with unusual spectra do not so much seem to 

 have peculiar elements as to be in peculiar physical 

 states. The universe seems, so far, of one make, and 

 there are no facts which negative the supposition that the 

 whole vast space through which we see stars is filled with 

 air; air very rare indeed, j^erhaps not a millionth of a mil- 

 lionth as dense as ours, but still, on the whole, similarly 

 constituted. 



FISH ACCLIMATIZATION ON THE PACIFIC COAST. 



BY HUGH M. SJnTH, M. D., UNITED STATES FISH COMMISSION. 



Few experiments in fish culture have been economically 

 more important and successful than those which have 

 been conducted by the United States Fish Commission 

 with reference to the Pacific Coast. Coincident with the 

 propagation of native fishes the introduction of non-indig- 

 enous species has been undertaken, with results that 

 have been extremely gratifying to fish culturists, and per- 

 haps more striking than any previously obtained in this 

 or any other country. 



Among the fishes inhabiting the rivers and coast waters 

 of the Atlantic sloj)e, none is better known, more import- 

 ant, and more highly esteemed than the shad (C'hqxa 

 sfflpicZ'is.9W)ia) and the striped bass or rockfish (Boccus 

 lineatus), the former being a food fish, pure and simple, the 

 latter combining a gamey disposition with excellent food 

 qualities. These fish are anadromous, entering the fresh 

 water for the purpose of spawning and jsassing a large 

 part of the year at sea or in the salt water. Attention 

 will be called to the experimental introduction of these 

 fishes to the west coast, although several other important 

 food-fish, among them the black bass {MicropteruH sal- 

 moides) and catfish {Ameiurus nebulosus) might also be 

 mentioned in this connection. 



The introduction of shad fry to the west coast was first 

 undertaken as long ago as 1871, when 12,000 young fish 

 were deposited in the Sacramento Kiver, under the aus- 

 pices of the California Fish Commission. After that the 

 exjjeriment was taken wp by the U. S. Fish Commission 

 and carried on until 1886, during which time 609,000 

 young shad were placed in the Sacramento Eiver, 600,000 

 in the Willamette Eiver, 300,000 in the Columbia Eiver 

 and 10,000 in the Snake Eiver. 



Two or three years after the first fish were filauted a 

 few more or less mature examples were obtained in the 

 Sacramento Eiver; as additional deposits were made, the 

 number of marketable fish began to increase, and the fish 

 gradually distributed themselves along the entire coast of 

 the United States north of Monterey Bay, until finally they 

 have come to rank next to salmon in abundance among 

 the river fishes of the west coast. 



The U. S. Commissioner of Fish and Fisheries, in his 

 annual rejaort for 1887, speaking of the small plants of 

 shad fry made in the Sacramento Eiver at Tehama, says: 



"From these slender colonies, aggregating less than one 

 per cent of the number now annually planted in our 

 Atlantic slojse rivers, the shad have multiplied and dis- 

 tributed themselves along 2,000 miles of coast from 

 the Golden Gate of California to Vancouver Island in 

 British Columbia. They are abundant in some of the 

 rivers, common in most of them, and occasional ones may 

 be found everywhere in the estuaries and bays of this long 

 coast line. 



"Prior to our experiments on the west coast it was a 

 dictum of fish culture that fish planted in a river would 

 return to it when mature for the j^uri^ose of spawning. 

 The result of these experiments has been to demonstrate 



