36 



SCIENCE. 



[Vol. XXII. No. 546 



tage in using the Thomson, even under the most favorable condi- 

 tions, and under ordinary circumstances there is no comparison 

 between them, the D'Ar.-onval type being absolutely unaffected by 

 external magnetic disturbances. Moreover, a good Thomson costs 

 at least $400, and an Ayrton-D'Arsonval only about $70. 



Whether this form of galvanometer will be equally satisfactory 

 when used for ballistic measurements does not, as yet, apppar. 

 There does not seem to be any reason why, with a good design and 

 a containing tube of hard rubber instead of silver, it should not 

 be perfectly satisfactory. 



Several sets of improved portable testing instruments for meas- 

 uring capacity and insulation of cables, etc., are worthy of atten- 

 tion. Full fets of the instruments of Lord Kelvin are al«o shown. 



Another exhibit, which may well make an American feel proud 

 of the work which is being done in this country, is the display of 

 the Weston Instrument Company. True it is that Mr. Weston is 

 an Englishman, but the perfection of the instruments is due, not 

 only to Mr. Weston's ingenuity, but also, to a large extent, to 

 American machine-shop practice. No other country can hope to 

 compete with us until they learn to use the fine and accurate 

 machine tools which till the instrument shops here. The writer 

 bad the opportunity a short time ago of visiting some of the more 

 celebrated European works for the making of electrical and physi- 

 cal instruments, There was not a universal grinder to be seen in 

 them, and in only one was a modern milling machine to be found, 

 and then but a single one. All the last touches were put on by 

 hand, and the result may be seen in the instruments theuifelves, 

 where every screw has to be marked, because no screw will fit 

 accurately into any hole except the one it is made for, and no two 

 parts of the same type of instrument are interchangeable. Tn 

 Europe, all the fine work is done in the assembling, here the 

 greater part is done before the instrument reaches the assembler's 

 hands. Probably there is no instrument in the world whose me- 

 chanical make-up is so perfect as an ordinary Weston voltmeter. 

 A number of new designs are shown, and the new laboratory 

 standards are especially fine. 



The long-looked-for manganin wire bridges hare begun to ap- 

 pear, the smaller portable testing sets being now on exhibition. 

 , This manganin wire is, as the reader is probably aware, the io- 

 Tention of Mr, Weston, having been discovered by one of his 

 assistants, Mr. John Kelly, while experimenting on that line. 

 There are a number of varieties of this alloy, which is formed of 

 different proportions of copper, nickel, and manganese. Some 

 of these have a negative coefficient, others a slight positive one, 

 and an intermediate class, no temperature coefficient at the ordi- 

 nary temperatures of working. The researches of the German 

 Government Standardizing Bureau have shown that the alloy is a 

 permanent one, and that it is well adapted for use in standard 

 jesistances. It is understood that new bridges of the latest im- 

 proved form, with four and five dials, are soon to be put on the 

 market, made of this wire, and accurate to a small fraction of a 

 per cent. Another new thing, soon to be put out, is the Weston 

 cadmium standard cell. It is well known by those who have done 

 "work on solutions that the solubility of a number of the cadmium 

 salts is the same at all temperatures within the ordinary range of 

 working Also that there is a relation between the solubility 

 and the voltage production of a solution. Mr Weston has utilized 

 this property of the cadmium salts to form a cell (of a similar 

 nature to the ordinary Clark cell, but with cadmium substituted 

 for the zinc and zinc salts), whose temperature coefficient is prac- 

 tically nil. It is claimed that considerable usage has shown that 

 it is very reliable. 



As regards the electrical fountains, there is little to be said of 

 them in spite of the great secrecy in which they ate wrapped by 

 the officials in charge. The principle is the one generally used, 

 i.e., the projection of a beam of light so as to strike the walls of 

 the jets from the inside, and so be reflected up along the inside 

 of the column of water. Some slight mechanical ingenuity has 

 been exercised in the means of feeding the carbons of the electric 

 arcs, otherwise there is little of interest in the mechanism itself. 

 The display, however, is very pretty, and it may be worth while 

 rto give a hint as to the best means of seeing it, as follows: — 



Take the electric launch at the wharf on the Liberal Arts side 



of the bridge connecting the Administration Building with the 

 Liberal .Arts Building, at about 8.30 or 8.15 in the evening (the ex- 

 act time depending upon the time the electric fountains begin to 

 play, the time of starting should be about 45 minutes before they 

 begin). This will bring the launch back to the basin containing 

 the fountains just about the time they are in full operation, and, 

 as the boats make two turns round this lagoon, opportunity is 

 afforded for a long view of the display. Moreover, the voyage 

 around the other lagoons gives one a beautiful view of the grounds 

 and buildings from the water. The illumination of buildings is 

 well under way by that hour, and the long ride on the water is 

 very enjoyable after the heat of the day. The writer has been 

 informed by those who have had the opportunity of comparing 

 the two, that even the most gorgeous sights of Venice do not enter 

 into comparison with the view thus obtained. R. A. F. 



A NEW INSTANCE OF STREAM CAPTURE. 



BY HUNTER L. HARRIS, CAMBRIDGE, MASS. 



The action of a rapidly flowing stream in cutting back into the 

 drainage area of another, of less gradient, and. finally, capturing 

 some of rts headwaters, has been prettily described in the columns 

 of this journal by Prof. W. M. Davis of Cambridge, under the 

 name of "A River-Pirate." In this notice he describes an' 

 instance of such action occurring in eastern Pennsylvania, and 

 alludes also to other instances, one of which is that occurring in 

 the Upper Engadine of Switzerland.' 



By keeping in mind the principles governing the cutting power 

 of streams, we may easily picture to ourselves the conditions 

 which would result from the excessive action of one stream over 



that of a near neighbor. Briefly, the more active stream, by 

 virtue of its greater activity, would begin to enlarge its catch- 

 ment basin, its headwaters eating their way gradually backward, 

 and so pushing the divide farther and farther into the region 

 formerly drained by the relatively weak stream. In process of 

 time, the aggressive stream may actually lap some of its 

 neighbor's headwater members, and, since the divide migrates 

 unevenly, this tapping may occur either at the head, or at some 

 point lower down on the invaded stream. If at the head, we 

 may have a short inverted stream, which possesses few marks by 

 which we may afterwards read its history. But if the connection 

 takes place lower down, as is often the case, a peculiar back-set 

 direction is given to the stolen tributaries which have been thus 

 forced to discharge their waters through a new main stream of 

 reverse direction. They may be compared to the barbs upon an 

 arrow, the body of the arrow representing the pirate stream. 

 This then constitutes a peculiarity by which we may easily 

 recognize instances of such capture. But other evidence should 

 be sought, such as the former comparative activity of the two 

 principal streams, indications of the former course of the stolen 

 tributaries, etc. 



The case of the Upper Engadine mentioned above may be 

 taken as typical. Here the aggressor is the Maira, flowing 

 southwest, and it has not only taken a goodly part of the drain- 

 age area of the Inn, which has an opposite direction of flow, but 

 has also appropriated at least three of its tributaries. The Maira 

 is considerably more rapid, and hence more active, than the other. 

 The accompanying sketch, taken directly from one of the maps 

 of the Swiss official topographic survey, shows the characteristic 

 form of the resultant drainage system. 



> Vol. xlil., 1889, p. 108. See also R. de C. Ward, " Anottier River-Pirate," 

 vol. xlx., 1891, p. 7. 



