NOVEMBEI! 23, 18S3.] 



SCIENCE. 



689 



for the purpose by Capt. Abney, and containing only 

 chloride of silver, has been generally used for the 

 sensitive plate. This film is said to be sensitive only 

 to rays between h and //, oral least to be only slightly 

 affected by rays of either higher or lower refrangi- 

 bility. Between April 2 and Sept. 4, fifty plates have 

 been exposed on fifteen different days ; and all of 

 them are said to show a more or less distinct coronal 

 appearance around the sun. 



The plates have been put into the hands of Mr. 

 Wesley, the celebrated engraver, who made the mag- 

 nificent plates of Mr. Kanyard's Eclipse volume ; and 

 he has prepared for each d.ay a drawing of what he 

 could make out on all the plates taken on that day. 

 " This was desirable," as Dr. Huggins says, "because, 

 whenever sufficient duration of sunshine permitted, 

 photographs were taken on silver-bromide films as 

 well as on silver-chloride plates: some photographs 

 were taken with the sun screened off by a brass disk 

 (close to the plate), others without it: also photo- 

 graphs were taken with the sun in different portions 

 of the field. As a rule, Mr. Wesley has introduced 

 into his drawings only those coronal features which 

 were common to all the plates taken on that day." 



Four drawings were presented, each of them show- 

 ing incontestibly details belonging to the lower por- 

 tion of the corona. The paper was jiresented to the 

 British association. — (Brit, journ. phot., 188:3, 57.5.) 

 V. A. Y. [380 



Saturn. — Dr. William Meyer of Geneva gives the 

 results of a large series of measures of Saturn and 

 his rings. The measures agree very well with those 

 taken in 1880. He also determined the position of 

 the belt in the southern hemisphere of the planet. 

 Encke's division was observed several times, and its 

 position seemed to be nearer the exterior edge on the 

 left than it was on the right ansa. On one occasion 

 the ball seemed of a grayish-blue tint, while the ring 

 was glittering white in color. — {Astr. nachr., 2,.5n. ) 

 Jt. MCN. [381 



MATHEMATICS. 



Equations of equilibriuni. — M. Appell remarks 

 that the analogies between the equations of equilib- 

 rium of a flexible and inextensible thread, and the 

 equations of motion of a point, have long been noted, 

 but that no one has put these equations of eciuilibri- 

 um into their canonical form, which would permit 

 the application of Jacobi's principles. M. Appell con- 

 siders first the case of a free thread acted on by forces 

 possessing a potential, and transforms the equations 

 of equilibrium into forms analogous to those giving 

 the motion of a point. He next introduces tlie no- 

 tion of generalized co-ordinates, </,, q,, q „ replacing 

 X, y, and z. The transformations made here are quite 

 similar to those given by Jacobi, in his Vorlesunijen 

 iiber dynamik. The author finally studies the position 

 of equilibrium of a thread acted upon by the s.ame 

 forces as before, but constrained to lie upon a given 

 surface. —(Co»ij)<es rendu.?, March 12.) T. c. [382 



Parallel surfaces. — Mr. Craig gives expressions 

 for the ratio between the corresponding elements of 

 area on a given surface and its parallel. The rela- 

 tions between corresponding elements of length, and 



the relation connecting the measures of curvature 

 on both surfaces, are also derived. The area of the 

 p.'irallel to the ellipsoid is obtained as the sum of 

 the areas of the given ellipsoid, a certain derived 

 ellipsoid, and a sphere whose radius is the modulus 

 of the parallel surface. — {Journ. fiir math., 188:!.) 

 T. c. [383 



ENGINEERING. 



Simple and compound engines on short 

 routes. — Mr. Boulvin has determined a series of 

 formulas expressing the relations between size of 

 vessel, weights carried, and distances traversed, and 

 the weights of the simple and the compound engine, 

 and finds, that, for short routes, the best form of en- 

 gine is the single cylinder rather than the compound. 

 He finds that for lines from twenty to sixty miles 

 in length, as those from Dover to Calais and from 

 Ostend to Dover, a gain of a knot an hour may be 

 obtained by the use of the simple engine instead of 

 the compound, in consequence of the saving in 

 weight of machineiy. On long routes the economy 

 is on the side of the compound engine, in consequence 

 of the saving in weight of fuel. The later practice 

 of English constructors has been in accordance with 

 this result, and with the principles involved in the 

 work of Mr. Boulvin. He constructs curves showing 

 the equations graphically, and illustrates their use by 

 examples. — {Ann. trav. publ., jlU.) k. ii. t. [384 



Transportation by steamers on the Rhone. — 

 Mr. F. Moreaux has investigated the conditions uf 

 transportation by steam on the Rhone and other fast- 

 running and shallow rivers, and has incidentally 

 developed a new formula for the resistance of vessels, 

 which he applies in his study of the best methods 

 of transporting merchandise. 



He takes an expression of the form 



B - Ki S' + K. X ~ X S", 

 - P 

 in which J? is the resistance, Kj and K... are numerical 

 coeflicients, iS" and S" are the areas of the middle 

 body and of the tapered ends of the vessel : I and p 

 are the length and the breadth of these ends. The 

 values of the coeflBcients vary, according to stated 

 conditions, from 0.10 to 0.22 for A', , and from 0.4S to 

 above 2 for K.,. They can only be used, evidently, in 

 cases in which these conditions are definitely known. 

 Where used as by Mr. Moreaux, however, they give 

 very satisfactory results. The formula is applied 

 to a river-navigation, now conducted largely with 

 steamers about 135 metres long, 7 wide, 1 metre in 

 draught, with 8 square metres area of immersed mid- 

 ship section, 1,100 square metres area of wetted sur- 

 face, and 900 tons displacement. Their engines are 

 of 1,150-horse power, ami their speed is about 4J 

 metres per second. The current is, in places, nearly 4 

 metres. Mr. Moreaux concludes that the best system 

 for such river-transportation is that in which is used 

 what he calls the ' Bateau mixte a ancres,' which is 

 fitted as a towboat, but which is also supplied with 

 anchors of peculiar form and of great holding-power, 

 by which the tug may be held at the head of a rapid, 

 and then, by hauling in a tow-line attached to the 

 tow, bring the latter through into still water. Two 



