24 



SCIENCE. 



[Vol. X. No. 231 



■constant velocity of the spherical wave, and the other the decreas- 

 ing velocity of the surface or emergent wave. By connecting 

 these points by rectangular co-ordinates, an equilateral hyperbola 

 is developed, the centre of which is the focus x, and the character of 

 which depends on the depth of the focus. The hyperbola becomes more 

 and more triangular in form as the depth becomes less (as in taking 

 the surface at c'd', c"d"), until, if the focus is at the surface, the 

 hyperbola becomes a right-angled triangle ; i.e., the surface wave 

 passes over equal spaces in equal times. If, therefore, we plot ac- 

 curately the times on AB, and the corresponding places on CD, 

 we may develop the hyperbola and calculate its centre ; or else by 

 accurate trial we may find a point which shall be the centre of 

 circles passing through corresponding times and places. That 

 point will be the focus. Such is a very general account of the 

 method, given in my own way. For more accurate detail, See- 

 bach's work must be consulted. 



We believe that this method, in a thickly settled country dotted 

 over with observatories on railroad-stations where accurate time is 

 kept, will prove the most accurate. Dutton and Hayden object to 

 this method that it is important to have the accurate time of arrival 



•of the wave, because there are two kinds of waves, — the normal 

 and transverse, — which run with different velocities. The answer 

 to this is, that it is only over a comparatively small area that, on any 

 method, observation can be relied on for estimating depth. In- 

 spection of Fig. 3 shows that the arm of the hyberbola very soon 

 becomes almost straight ; the velocity of emergence at any con- 

 siderable distance becomes sensibly the same as that of the spher- 

 ical wave, and therefore can no longer indicate depth. But over the 

 small area where the curve of the hyperbola, or change of velocity, 

 is rapid, the time of arrival of the different waves would not greatly 

 differ. At any rate, the use of seismographs which decompose the 

 complex earth-motions will record these different waves separately, 

 and thus enable us to determine the law of decrease of one of them 

 — the normal — with accuracy. 



In conclusion we would insist that we cannot any longer afford 

 to study earthquakes without seismographs. The Geological Sur- 

 vey ought to have these in different parts of the country. The 

 University of California has recently gotten three of these of the 

 best character (Swing's and Gray-Milne's), which will soon be set 

 up in different parts of the State. Joseph LeConte. 



Berkeley, Cal., June 21. 



The Corresponding Volumes, etc., of Ice and Sea-Water. 



These determinations were made in Hudson Strait (latitude 

 62° 33' 45" north, longitude 70° 41' 15" west), in an inlet having a 

 width of a little more than half a mile. I am thus particular in 

 giving the width, because in a very narrow tidal harbor, with the 

 ice fast on either shore, the line of flotation of the ice would sensibly 

 alter with a rising or falling tide. In this instance I was particular 

 in watching for such a difference, under these opposite conditions ; 

 but, if present, it was insensible. 



The determination was made on Feb. 3, 1885, when the temper- 

 ature of the air was — 3° F. ; for the water, 36°. 7 F. 



A hole having been cut through the ice, of such a size as to pre- 



vent any sensible error owing to capillarity, its thickness was found 

 to be 2 feet 9.6 inches from surface to surface ; on top of the ice 

 was an estimated average depth of snow of 3 inches, of such a 

 density that by weight it was equal to i.i inches of the ice : the 

 total thickness of ice, or its equivalent, would therefore be 2 feet 

 10.7 inches. Of this amount, 32.5 inches were submerged ; leaving, 

 therefore, 2.2 inches of ice, or its equivalent, above the water-line. 



Therefore sea-water-ice floats with one part above the water- 

 line and fourteen and eight-tenths below. Expressingthe volume of 

 a given quantity of sea-water by unity, its volume, when converted 

 into ice, would be 1.0634; and their densities as 0.922 to i.ooo. 



W. A. Ashe. 



The Observatory, Quebec, June 24. 



Death of W. O. Ayres, M.D. 



The death of Dr. W. O. Ayres, one of the early members of the 

 California Academy of Sciences, has recently been made known. 



He was specially interested in the study of ichthyology, and for 

 many years after his arrival in California, in the intervals of an ex- 

 tensive medical practice, contributed to this department of natural 

 history by his investigations of and publications upon the fishes of 

 California. At the first meeting of the academy of which there is 

 any published record, Sept. 4, 1854, he presented descriptions of 

 two new species, Labrics pidcher and Hemitripterus marmoratus, 

 which still stand, though the generic status has been modified, — 

 now Harpe pitkhra and Scorcenichthys marmoraiits. His con- 

 tributions to the ichthyological knowledge of the Pacific coast 

 were frequent for many years, especially from 1854, as above, to 

 the year 1863. His scientific inquiries sometimes extended, though 

 rarely, towards other forms of animal life. He returned to his 

 native State, Connecticut, about 1872 or 1873. His services to the 

 cause of science on the Pacific coast in those early days entitle 

 him to grateful remembrance. R. E. C. S. 



U. S. Nat. Mus., June 28. 



Cause of Consumption. 



The experimental together with the clinical study of tuberculo- 

 sis has established the view that there are three factors in its 

 causation : — 



First, The presence of the parasite, the tubercle-bacillus, as a 

 pathogenic element. This factor is necessar}' for the production of 

 the disease. 



Second, Heredity figures as a prominent element in about thirty 

 per cent of the cases ordinarily met with. 



Third, Mal-hygienic and debilitating agents, such as foul air, 

 sedentary occupations, violations of the laws of health, and dis- 

 eases, have a powerful effect, by impairing the nutrition, in develop- 

 ing the disease. 



Heredity and lowered vitality cannot of themselves produce 

 tuberculosis, but clinically they play an important 7-dle as factors by 

 rendering the individual more vulnerable to bacillary influence. 



Frank Donaldson, M.D. 



Baltimore, Md., June 29. 



Volapuk. 



Your correspondent, ' H. T. P.,' in your issue of the 24th of 

 June, asks for information about Volapuk. I can refer him to a 

 most interesting article upon this subject, which appeared in the 

 BiMetms de la Socieie d' Ajithropologie de Paris, 1885, pp. 317- 

 321. The article is by M. Kerckhoffs, who has published the fol- 

 lowing work, ' Cours Complet de Volapiik,' par A. Kerckhoffs 

 (Paris, 1886), and contains a sketch of the structure of the lan- 

 guage and some interesting information about its prospects, prog- 

 ress, etc. A. F. Chamberlain. 



Toronto, June 28. 



Queries. 



7. Deaths and the Tide. — A physician living near the sea 

 states that during the past five years he has noted the hour and 

 minute of death in ninety-three patients, and every one has gone 

 out with the tide, save four who died suddenly by accident. Is 

 there any other evidence to sustain this statement ? — D. 



