July 1, 1897.] 



KNOWLEDGE. 



169 



of commercial machinery, or are too strictly theoretical, to 

 be of value to the practical electrician. This volume does 

 not err in either of these directions. It happily combines 

 theory and practice, dealing instructively with the funda- 

 mental phenomena of alternating currents as well as 

 their applications. A text-book so planned, and which 

 passed through the refining fire of the lecture-room before 

 it was put into type, cannot but be satisfactory. These 

 qualifications are sufficient to convince teachers and 

 students of electrical engineering that the work of Profs. 

 Jackson is one which should not be overlooked. 



SHOKT NOTICES. 



English Literature from A.D. 670 to A.D. 1832. By Stopford A. 

 Brooke, M.A. (Macmillan & Co.) Is. This is a reprint of Mr. 

 Stopford Brooke's scholarly survey of English literature, originally 

 issued as one of the Literature Primers, edited by the late John 

 Richard Grecu. It has been largely revised and corrected by the 

 author, and contains a fidl chronological table and index to authors. 



The Months, descriptive of the Successive Beauties of the Year. 

 By Leigh Hunt. With Biographical Introduction by William 

 Andrews, F.E.H.S. (London: William Andrews & Co.) 2s. This 

 is a reprint of a delightful little book which originally appeared in 

 1821. We are glad to welcome its re-issue, though for a totally 

 different reason to that quaintly given by the editor, that when 

 offered for sa'e the original issue fetched ten times its published price. 

 Leigh Hunt's sunny nature and gentle bearing, his delight at the 

 simplest beauties of nature, and his observant contemplation of her 

 moods, go to make a happy book, and a happy reader, too. 



We have received from Messrs. Houghton & Son a very comprehen- 

 sive and well-illustrated price list of photograpliic apparatus and 

 materials. It seems to contain a list of everything requisite to a 

 photographer, from cameras, lenses, and shutters, to plates and 

 papers, by all the best manufacturers. 



The Ellipsograph. By T. Moy. (W. H. Harling.) 30s. 

 Draughtsmen of all kinds — mechanical, architectural, the engraver — 

 know the value of any contrivance which will facilitate the construction 

 of that innoceut-looking curve, the ellipse, which, nevertheless, is 

 most troublesome to draw, even by the approximate methods in vogue, 

 and hence, on account of its frequent reciu'rence, absorbs much 

 valuable time. We have before us a neat and efficient piece of 

 apparatus— the ellipsograph — which enables one to draw ellipses of 

 every degree of eccentricity with as little trouble as is involved in 

 describing a circle with a pair of compasses, and, at the same time, 

 absolutely accurate. Eeferring to the figure, a pencil or pen is 

 inserted in the graduated vertical tube and secured by a spring 

 operated by a screw ; the semi-axis major is set off by turning the 

 screw of the graduated regulator (on the right) till the arrowhead has 

 moved outwards the required distance from zero, which is exactly 

 over the centre of rotation, and a vertical screw actuating the diagonal 

 limb, which slides telescopically as the angle of inclination varies, is 

 adjusted so that the extreme lateral point of swing coincides with the 



BOOKS RECEIVED. 



Through a Pocket Lens. By Henry Scherren, F.Z.S. (Religious 

 Tract Society.) Illustrated. 2s. 6d. 



Lepidoptera. By W. P. Kirby, F.L.S. Allen's Naturalists' Library. 

 Edited by R. Bowdler Sharp. (Allen & Co.) Illustrated. 6s. 



Hi/pnotism and its Application to Practical Medicine. By Otto 

 Georg Wetterstrand, M.D. (Putnam's Sons.) Illustrated. 10s. 



Practical Histology. Second Edition. By Edward Albert Schafer, 

 LL.D., F.R.S. (Smith, Elder.) lUustrated. 7s. 6d. 



Some Unrecognized Laws of yatiire. By Ignatius Singer and 

 Lewis H. Bereus. (Murray.) Illustrated. 18s. 



The Induction Coil in Practical M'ork, including Rontgen X Pngj. 

 By Lewis Wright. (Macmillan.) Illustrated. 49. gd. 



Poems for the Schoolroom and the Scholar. Masterpiece Library. 

 Arranged by Robert S. Wood. (Reeiew of Rerieics Office.) 6d. net. 



Proceedings uf the Academy of Natural Sciences. Part III. 

 Edited by E. J. Nolan. (Logan Square, Philadelphia.) Illustrated. 



The Migration of Birds. By Charles Dixon. Amended Edition. 

 (Horace Cox.) Maps. 



Bird Life. By Frank M. Chapman. (Applcton, New York.) 

 Illustrated. 



Grnndprobleme der Naturicissenschaft. By Dr. Adolf Wagner. 

 (Borntracger, Berlin.) 



Life in Harlg Britain. By Bertram C. A. Windle. (Nutt.) 

 Illustrated. 3s.' fid. 



Chess Openings. By James Mason. (Cox.) Illustrated. 2s. n t. 



Sound, Light, and Seat. By Wm. Briggs. (Clive.) Illustrated. 2s. 



Lessons in Elementarg Practical Physics. By C. L. Barnes. 

 (Macmillan.) Illustrated. 4s. 6d. 



Outlines of Physics. By Edward L. Nichols. (Macmillan.) 

 7s. fid. 



Elements of Vescriplice Astronomy. By Herbert A. Howe, D.Sc. 

 (Silver, Burdett, & Co., New York.) Illustrated. 7s. 6d. net. 



Smithsonian Report, 1S95. (Grovernment Printing OfEce, Washing- 

 ton.) 



The Naturalist in Australia. By W. Saville-Keut, F.L.S. , F.Z.S. 

 (Chapman & Hall.) Illustrated. 63s. 



outer limits of the minor axis. By now rotating the regulator, using 

 the milled head as a handle, the diagonal piece slides longitudinally, 

 and the top horizontal bar rocks laterally, the compound motion thus 

 imparted to the pencil resulting in a most accurate elliptical curve. 

 The angle of the diagonal bar may be diminished till practically 

 horizontal, in which case circles are traced out. The instrument can 

 be used with great advantage for draiving wheels, etc., in perspective. 

 We may add that it is easily and quickly re-adjusted for drawing all 

 sizes of ellipses within the range of the instrument, which, of course, 

 is limited. As a piece of mechanism it does great credit to the 

 inventor and maker alike. 



THE HOURGLASS SEA ON MARS. 



By E. M. Antoni.^di. 



THE most interesting, characteristic, and by far the 

 most easily recognizable feature of the planet 

 Mars is the great, dark, triangular spot of its 

 northern hemisphere, known as the " Hourglass 

 Sea." 

 No name could have been more appropriate to this 

 marking, not only for the close resemblance the spot bears 

 to an hourglass, but also from the fact that it was the 

 Hourglass Sea itself which acted as hourglass in the 

 determination of the rotation of Mars on its axis. 



The name has, however, dropped out of use, having 

 been superseded by the names given by successive 

 areographers. Thus Proctor, in his map of 1867, calls 

 it the " Kaiser Sea " (a name adopted by Green in 

 1877) ; others named it the " Northern Sea " or 

 "Dawes' Bay " ; while Schiaparelli, who has furnished 

 the markings of the planet with a brand new set of 

 names of his own, calls it the " Syrtis Major," 

 although there is not the slightest trace of likeness in 

 the outlines of the Hourglass Sea on Mars and the 

 Major Syrtis of our own earth. 



In general outline the Hourglass Sea is not unlike 

 India, whose Indus and Himalayas would correspond 

 to the " pontes," or whitish " bridges," to which Mr. 

 Lowell called attention in 1894. The total length of the 

 eastern* shore is some thirty degrees ; that of the weste in 

 forty degrees. To the east the shore follows very nearly 

 the two hundred and eighty-second meridian, then curves 

 eastwards into the Lesser Syrtis. The semicircular land 

 formed by this curve is called Libya by Schiaparelli, and 



* We are using the words " east " and " west " in their areographical 

 sense. Thus, of two markings, the preceding is the eastern, the 

 following the western. 



