Apkil C, 1SS3.] 



SCIENCE. 



255 



from the Probelie/t of the new mathematical journal 

 edited by G. Mittag-Zeffler in Stockholm. — {Acta 

 math., i.) t. c. [535 



Definite integrals. — M. DavidofE obtains two 

 very general formulae, depending upon an arbitrary 

 fimction F (x) of the nth degree in x- He claims, by 

 aid of these, to be able to obtain nearly all of the 

 known theorems concerning definite integrals, by 

 making Ji infinite, and properly choosing the form of 

 F [x)- Several applications are made, based upon the 

 assumption of particular forms for F {x)- — (Journ. 

 demath.,lSS-2.) t. c. [536 



PHYSICS. 



New method of determining specific gravity 

 of solids. — Professor Munroe, having occasion to 

 ascertain on shipboard the specific gravities of sam- 

 ples of coal, and being prevented by the motion of 

 the vessel from using the balance, devised a procedure 

 which not merely served his purpose, but is suscepti- 

 ble of wide application. Placing a block of coal in a 

 liquid so dense as to float it, he gradually reduced the 

 density by the admixture of a lighter liquid, until the 

 coal floated immersed. The homogeneity of the mix- 

 ture being maintained by stirring, this equilibrium 

 was, of course, reached only when the specific gravity 

 of the liquid became equal to that of the immersed 

 solid. He then measured the specific gravity of the 

 liquid with a common hydrometer. For the flotation 

 of the lighter coals, he used a thick solution of cane- 

 sugar; for anthracite, strong sulphuric acid. 



As a test of the accuracy of the results, he after- 

 ward repeated the determinations with Jolly's balance, 

 obtaining, — 



{Phil. soc. Wash. ; meeting March 24. 



[537 



Domestic thermometry. — M. Gaston Tissandier 

 considers tlie errors that are likely to be made in de- 

 termining the temperature of a room by the usual 

 method of a thermometer hung on the wall. He 

 found that the apparent temperature of a closed 

 room varied from 1G° to 21.75°, according to the 

 position of the thermometer. The air in the upper 

 part of the room was much warmer than that near 

 the floor, and the window had a very marked effect 

 on the temperature of the air in its vicinity. 



These observations were made with tested ther- 

 mometers. The errors made with tlie ordinary domes- 

 tic thermometer are, of course, much greater. 



In order accurately to obtain the temperature of a 

 room, M. Tissandier advises the thermometer to be 

 held at the height of a man for about two minutes at 

 several different points, and the mean of these obser. 

 vations to be taken. — ( La Nature, No. 508. ) c. B. p. 



[538 

 Electricity, 



Determination of resistance-unit. — Lord Ray- 

 leigh recently read a paper before the Eoyal society, 



describing experiments conducted by him on the 

 value of the B. A. uuit of resistance. Three series of 

 observations were taken, — two by Lorentz's method, 

 and a third, in which the induction coils were sepa- 

 rated from the disk so far that the result was ]3racti- 

 cally independent of the radius of the coils. The 

 mean value obtained was 



1 B. A. unit = .98677X10" (c. G. s.). 

 The standard of time was a tuning-fork, whose abso- 

 lute pitch was determined by a new method. — (Elec- 

 trician, Feb. 10.) J. T. [539 

 Pressure and resistance in carbon. — S. Bid well 

 read a paper before the Eoyal society, giving the re- 

 sults of experiments on carbon cylinders making con- 

 tact at riglit angles with eacli other. He proves that 

 changes in pressure produce the greatest proportional 

 effect when the pressure and strength of current is 

 comparatively low; on the removal of the pressure, 

 the resistance returns to about its original value. 

 The passage of a current tlie strength of which does 

 not exceed a certain limit causes a permanent dimi- 

 nution of tlie resistance. Similarly, the lessening of 

 resistance due to pressure is magnified by tlie action 

 of the current. — J. T. ' [540 



ENGINEERING. 



The Antwerp ■water-works. — Mr. William An- 

 derson recently read a paper at the Institution of 

 civil engineers in London, which contains some in- 

 teresting facts in regard to the purification of water 

 for domestic purposes. Antwerp has 200,000 inliabit- 

 ants, and until recently its water was derived from 

 shallow wells and from open canals. The well-water, 

 though clear to look at, was for tlie most part dan- 

 gerously contaminated by the sewage. The new 

 works take the water from the Nfetlie at a point eleven 

 miles from Antwerp. This water was very impure, 

 even after ordinary filtration through sand, as the 

 river flowed through a highly cultivated country, 

 carrying up the drainage of Malines on the flood-tide, 

 and bringing down that of the villages on its upper 

 waters on the ebb. The time during which water 

 could be taken was thus limited to about three-quar- 

 ters of an hour in each tide. Prof. Bischoff, Dr. 

 Frankland, and Mr. Hatton had shown that finely 

 divided metallic iron had the power of destroying 

 organic impurities, removing color, separating finely 

 suspended matter, and, above all, destroying the germs 

 of putrefaction, of bacteria, and probably those of 

 epidemic diseases. To confirm the laboratory evi- 

 dence, a ijair of filters with a total area of 680 square 

 feet was made at Waelhem; the first filter being 

 placed upon a higher level than the second, and filled 

 with a bed of spongy iron and gravel, mixed in the 

 proportion of one to three, covered with a layer of 

 ordinary filter-sand. In this filter the water would 

 become charged with iron, to eliminate which it was 

 to be exposed to the air, and passed through a second 

 or common sand-filter, in which the red oxide would 

 be deposited. Three months of trial proved so satis- 

 factory that three filters of the same kind were made, 

 having an aggregate area of 31,000 feet, with three 

 sand-filters of the same area. Eighteen months' work 

 has shown that, the water remains clear and bright, 

 while the spongy iron showed no signs of deteriora- 

 tion. Dr. Frankland reports favorably upon the 

 chemical condition of the water, and also upon the 

 complete destruction of bacteria and their germs. — 

 {Van Nostrand' s marj., March, 1SS3.) G. L.V. [541 



Seasoning ■wood for musical instruments. — 

 Mr. C. Rene of Stettin has devised a process for the 

 drying of wood, intended especially for the prepara^ 



