June 15, 1883.] 



SCIENCE. 



549 



Prof. Cayley adds an interesting note to tliis paper. 

 — (Quart. Journ. ma«/j., Feb.) t. c. [1067 



Optics. 



Reversal of hydrogen-lines. — Liveing and 

 Dewar communicate to the Eoyal society an interest- 

 ing note, sliowing, tliat, wlien tlie induction-spark is 

 taken between electrodes of aluminium at a pressure 

 of two or three atmospheres, the reversal of F is 

 easily obtained ; that of C, only with difficulty. By 

 spirting fine drops of water with a pipette into the 

 electric are, the hydrogen-lines become brilliantly, 

 and, so to speak, ' explosively' visible for an Instant, 

 but without any reversal. — {Nature, May 3. ) c. A. T. 



[1068 

 {Photography.) 



Iodide of silver in the emulsion. — Herr Schu- 

 mann has been experimenting on emulsions sensi- 

 tized by combinations of the iodide and bromide of 

 silver. • Capt. Abney, Dr. Eder, and Dr. Vogel 

 found tliat the introduction of iodide diminished 

 rather than increased tlie sensitiveness of the emul- 

 sion, while Herr Schumann obtained the opposite 

 result. He now finds the cause of this discrepancy 

 to be. that wliile the former autliorities prepared 

 their iodide and bromide emulsions separately, and 

 then mixed tliera, in order to obtain accurate quan- 

 titative results, he has been in the habit of precipi- 

 tating the two togetlier in one and the same 

 solution, as would be done in the practical working 

 of the process. As prepared by the former metliod, 

 the emulsion is of a pale yellow color; while, by tlie 

 latter, it is darker and of a citron-yellow tint. The 

 sensitiveness nf tlie mixed emulsions is at a maxi- 

 mum in that piution of the spectrum lying between F 

 and G. It ha^ a lower maximum in the vicinity of 

 the II line, and is practically insensitive to the 

 region half way between G and h. The spectrum 

 of the cnmbined emulsion differs from the above in 

 having a distinct maximum between h and F, and 

 in its much greater sensitiveness to the less refrangi- 

 ble rays. — ( Brit, journ. phot., April 27. ) w. H. p. 



[1069 



Photographing the vocal organs. — Messrs. H. 

 T. Wood, Belmke, and Cadett liave recently suc- 

 ceeded in pliotographing tlie vocal organs in action. 

 An electric llglit and laryngoscope were employed. 

 It was necessary, in tliese experiments, to so arrange 

 the liglit, that the singer should at the same time be 

 enabled to see that the mirror was in tlie proper 

 Ijosition, and also that the image was reflected di- 

 rectly Into tlie camera lens. The light was placed 

 by the side of the camera, and a little in front of it ; 

 and tlie rays were directed by means of a condenser 

 upon a mirror placed immediately above the lens ; 

 this mirror being set at an angle of 4.5° so as to di- 

 rect the light upon the subiect. The condenser was 

 furnished on the side next the lamp with a water- 

 jacket, througli wliloli a current of water was Icept 

 flowing to prevent injury to the lens from the heat 

 of the lamp. The rays from the first mirror ^'ere 

 received upon tlie small laryngoscopic mirror placed 

 at the back of the throat, and the image formed in 

 this was reflected upon another small mirror fixed to 

 the front of a drop-shutter ; tlie object of tliis ar- 

 rangement being to enable the person whose organs 

 were being photograplied to see when the image was 

 properly directed. When this was done, lie gave the 

 signal to tlie operator, and the exposure was made. 

 In some of the latter experiments, arrangements 

 were adopted by which a pair of stereoscopic lenses 



could be used, one lens serving as a finder, and the 

 other producing the picture. — (Brit, journ. phot., 

 April 13. ) W. H. p. [1070 



Electricity, 

 Resistance of the electric arc. — Ayrton and 

 Perry, experimenting upon the electric arc between 

 carbon poles, employing at times a battery of Grove 

 cells, and at others a Brush dynamo, find, like 

 Schwendler, that the resistance of the arc, including 

 under this liead both the resistance proper and the 

 opposing electromotive force at the carbon surfaces, 

 is nearly inversely proportional to the current. The 

 following is given as a sample of the results obtained 

 from a number of tests with Grove cells: — 



Other experiments showed, that, when a given 

 current was trebled, the difference of potential be- 

 tween the poles was slightly Increased. Tlie authors 

 have also tested the relation between length of the arc 

 and the difference of potential between the poles. A 

 large number of experiments were made for this pur- 

 pose with a Brush machine, giving currents varying 

 between 5.5 and 10.4 amperes, the distance between 

 the carbon points varying between and Ij inches, 

 and the difference of potentials from to 140 volts, 

 the carbons being 0.24 inch thick. The results are 

 plotted, giving a curve for which the approximate 

 equation is, — 



-B = 63 -f- 55a — 63 X 10-m°, 

 wliere F is the difference of potentials in voltSj and a 

 tlie distance between the points in inches. — (Phil, 

 mag.. May.) e. h. h. [1071 



ENGINEERING. 



The steamer City of Fall River. — The steamer 

 City of Fall River, whicli has been recently added to 

 the Fall Eiver line between New York and Boston, 

 exhibits some decided innovations. The engine, of 

 2,000-horse power, was designed and built by Messrs. 

 A. & W. Fletcher of New- York City. It is a com- 

 pound beam engine, fitted with the Morgan feath- 

 ering paddle-wlieels, and supplied with steam by a 

 Redfieid boiler, all of which features are unusual. 

 The steam-cylinders are 44 inches diameter by 8 feet 

 stroke, and 68 inches by 12 feet stroke. The wheels 

 are 25 feet 6 inches in diameter. The boilers are 

 of Otis steel, and are tested to 150 pounds pressure 

 per square inch. The boat is 260 feet long, 41 feet 

 beam, 17 feet deep. Over the guards the breadth 

 is 73 feet. The draught of water, loaded with 600 

 tons of freight, is 12 feet. This steamer has made 

 the 181 miles from port to port in 10| hours, and 

 has made 17 miles an hour. The coal consumption 

 is small, — 20 tons per round trip. — (>S'c. Amer., 

 May 5.) P.. ii. T. [1072 



CHEMISTRY. 

 {Organic.) 



Oxidation of aromatic monamines and dia- 

 mines. — Wlien equal molecules of dlmetliylpara- 

 phenylendiamine and dimethylaniline in an aqueous 

 solution with zinc chloride were treated with the 



