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SCIENCE. 



[Vol. XIV. No. 360 



its properties, however long it was thus kept. There is no 

 static condition in heat phenomena : exchange is constant. These 

 facts indicate that light or radiant energy is no more an electro- 

 magnetic phenomenon than magnetism is a thermal phenomenon, 

 but that it is one of a distinct order. 



That point is inmaterial here, for what I wish to call attention to 

 is the fact that a heated body sets up in the ether such a physical 

 condition that its re-action upon another body brings the latter to 

 a condition similar to the first ; that is, it heats it. 



IV. The Acoustic Field. — There is another physical field with 

 which all are acquainted, though it has not hitherto been called by 

 that name. I refer to the phenomena of sound. Suppose a bell 

 be struck : sound-waves in air are formed, that travel outwards, 

 and have the same geometrical space relations that other fields have. 

 So long as the medium is uniform, the field is uniform, and the energy 

 of the sound-waves per unit surface and unit time varies inversely as 

 the square of the distance from the source. When such sound-waves 

 "fall upon other masses of matter, they are absorbed and reflected. 

 Those that are absorbed set the body in vibratory motion similar 

 to the original vibrating body ; that is to say, they produce sound. 

 If such second body upon which the waves fall happens to have its 

 own vibratory rate in accordance with the time- rate of the incident 

 waves, the effect is cumulative, and the body may be made to visi- 

 bly as well as audibly vibrate. If not, the vibrations are said to be 

 forced vibrations ; but in every case every body in an acoustic field 

 is made to vibrate. Now, there is the same distinction between 

 the vibratory motions of the bell and the air-waves that result from 

 them as there is between heated molecules and the undulations in 

 the ether ; but acoustical terminology has not hitherto been so se 

 Tiously incommoded hy the failure to make the distinction as has 

 ■been the case with heat phenomena. As sound phenomena are 

 treated as special cases in kinetics, the space within which sound- 

 waves are produced by the vibratory motions of a body may be 

 spoken of as the acoustic field ; and here, as in the other three 

 ■cases, we have the fact that a sounding body sets up in the medi- 

 'um about it such a physical condition as, by its re-action upon an- 

 other body, brings the latter into a vibratory state like the first. 



These various physical relations may be thus generalized : when 

 a mass of matter acts upon the medium that is about it, the latter is 

 thrown into such a physical conditition or state that its re-action 

 upon another body always induces in the second body a state simi- 

 lar to that of the first body. This has a much wider application 

 than most physical laws; for it embraces phenomena in mechanics, 

 iheat, light, electricity, and magnetism. A. E. Dolbear. 



Tufts College, Dec. st. 



The Waters of the Great Salt Lake. 



Long before white men first trod the shores of the Great Salt 

 Lake, strange stories of this inland sea had found their way 

 into the civilized regions of our own land, and even beyond the 

 ocean. The earliest record of the lake was made in 1689 by the 

 traveller, Le Hontan, who relied for his information upon the wild 

 tales told by the Indian tribes of the Mississippi valley. In 1843, 

 however, the lake was visited, its shores explored, and its waters 

 ■navigated, by Gen. Fremont, of extensive fame. Six years later 

 (1849-50) a fuller survey was made under the personal direction of 

 Capt. Howard Stansbury, U.S.A., whose report, " Expedition to 

 the Valley of the Great Salt Lake," issued at Washington in 1853. 



The Great Salt Lake is by far the largest body of water existing 

 in the " Great Basin." Its average length is seventy-five miles ; 

 and its width, forty miles. The altitude of the lake is near forty- 

 two hundred feet above sea-level, and the region is declared by 

 .geologists to be still rising. 



Even a hasty examination of the Salt Lake valley will convince 

 the observer that the present lake is but the shrunken remnant of 

 a vastly larger body of water, which at one time stretched far be- 

 yond the limits of the valley. This former sea was a feature of 

 ■quaternary times, and has been named Lake Bonneville. It ex- 

 tended beyond the Idaho line on the north, invaded Nevada on the 

 west, and closely approached the Arizona boundary on the south. 

 Of this great body, Utah Lake and Sevier Lake, now existing as 

 distinct occurrences in the regions south, were but comparatively 



small bays. Numerous water-lines are visible along the mountains 

 adjacent to the Salt Lake, the highest of which is about one thou- 

 sand feet above the pressnt water surface ; and the evidence of 

 wave-action along this ancient shore is abundant. 



The history of Lake Bonneville, as recorded on the stony pages 

 of its precipitous shores, and in the hardened sediments of its floor, 

 is more complicated than a mere recital of the shrinking and falling 

 of waters through evaporation and other wasting causes. For most 

 of our knowledge upon this subject, we are indebted to the detailed 

 observation and study conducted by the United States Government 

 Survey corps, and especially to the investigations carried on under 

 the direction of Major J. W. Powell. Referring to the labors of 

 Mr. C. K. Gilbert and his associates in the lake region, Director 

 Powell thus briefly summarizes the history of Lake Bonneville : — 



" First, the waters were low, occupying, as Great Salt Lake now 

 does, "only a limited portion of the bottom of the basin. Then they 

 gradually rose and spread, forming an inland sea, nearly equal to 

 Lake Huron in extent„with a maximum depth of one thousand 

 feet. Then the waters fell, and the lake not merely dwindled in 

 size, but absolutely disappeared, leaving a plain even more desolate 

 than the Great Salt Lake Desert of to-day. Then they again rose, 

 surpassing even their former height, and eventually overflowing 

 the basin at its northern edge, sending a tributary stream to the 

 Columbia River ; and, last, there was a second recession, and the 

 waters shrunk away, until now only Great Salt Lake and two 

 smaller lakes remain." 



As is clearly understood, the oscillations of the water in a lake 

 possessing no outlet will be far more marked than in an opposite 

 case. In a body of water with an outflow, a tolerably uniform 

 level will be maintained, the irregularities in the supply being com- 

 pensated for the most part by the varying volume of water flowing 

 away ; but the level of a lake completely enclosed will be due to 

 the relation existing between the supply of water and the rate of 

 evaporation. The topography of the ancient shore-line of the 

 Great Salt Lake shows, that since the time of the " second reces- 

 sion " of the waters, referred to by Major Powell in the quotation 

 made above, the lake has been unable to find an outlet for its con- 

 tents, and has consequently reached its present diminutive propor- 

 tions through loss by evaporation alone. The composition of the 

 water would necessarily vary with the concentration. The analysis 

 most commonly accepted, and which forms, indeed, the basis for 

 current quotations and references, is that made by Dr. Gale, and 

 published in Stansbury 's report. Gale found the water to possess 

 a specific gravity of 1. 170, and to contain 22.282 percent by weight 

 of solid matter, as follows: sodium chloride (Na CI), 20.196 per 

 cent; sodium sulphate (Na^ SO4), 1.834; magnesium chloride 

 (Mg CI3), 0.252 ; calcium chloride (Ca Cl^), a trace. 



These figures are used as indicative of the present composition 

 in several of the most recent cyclopeedias, such as are used for 

 general reference ; and even the revised school text-books in geog- 

 raphy quote as above. It should be remembered in accepting such 

 results, however, that the investigation upon which they are 

 based was made on water collected forty years ago ; and it is 

 scarcely to be expected that such would represent the composition 

 of the water at the present time. For a number of years preceding 

 1883 the lake had been steadily rising. This rise was entirely in- 

 dependent of the annual oscillations to which the waters of the 

 lake seem subject under all circumstances. In referring to this 

 fact, Mr. Gilbert writes as follows (see "Lands of the Arid 

 Regions," p. 66) : — 



" Thus it appears that in recent times the lake has overstepped 

 a bound to which it had long been subject. Previous to the year 

 1865, and for a period of indefinite duration, it rose and fell with 

 the limited oscillation and with the annual tide, but was never car- 

 ried beyond a certain limiting line. In that year, or the one fol- 

 lowing, it passed the line, and it has not yet returned. The annual 

 tide and the limited oscillations are continued as before, but the 

 lowest stage of the new regime is higher than the highest stage of 

 the old. The mean stage of the new regime is seven or eight feet 

 higher than the mean stage of the old. The mean area of the 

 water surface is a sixth part greater under the new regime than 

 under the old. The last statement is based on the United States 

 surveys of Capt. Stansbury and Mr. King. The former gathered 



