March 23, 1883/ 



SCIENCE. 



199 



Electricity. 

 Rotatory effect of terrestrial magnetism. — In 



187S H. Becquerel showed that the rotatory intlu- 

 ence of teirestrial magnetism on liglit traversing 

 gases could be accurately measured. The fundamen- 

 tal experiment consists in arranging uijon the same 

 horizontal support, movable about a vertical axis, a 

 soxu'ce of light, a polarizer, a column of the sub- 

 stance to be investigated, and an analyzer mounted 

 upon a divided circle. The axis of the column and of 

 the beam of light is placed in the magnetic me- 

 ridian, and the plane of polarization noted : the 

 apparatus is then turned end for end; the plane of 

 polarization is still the same, but the divided circle 

 has been turned about, so that the" apparent ro- 

 tation is reversed. The effect was multiplied by 

 successive reflection from mirrors at the end of the 

 column of gas, and also by interposing a thin crys- 

 talline plate, which rotated the plane of polariza- 

 tion symmetrically about the axis of the crystal. 



The author found that the plane of polarization of 

 the luminous rays, D, is rotated through .943.5' in 

 traversing 1 metre of CS-7 at 0° C. under the influ- 

 ence of terrestrial magnetism, and that between two 

 points 1 cm. distant, in a magnetic field of strength 

 unity (c. G. s. ), the rotation of the same rays in 

 passing through CS, at 0° C. is .0463± .0004. Thus 

 he claims he can measure, by an optical determina- 

 tion, the intensity of any magnetic field whatever 

 to Tou of its value. — (^-Inji. chim. phys., Nov., 1882. ) 

 J. T. [420 



Electric discharge in rarefied air. — Edlund con- 

 tinues his investigation of this subject. He connects 

 the combs of a Holtz machine by means of a wire 

 interrupted by a short air-space. The circuit con- 

 tains in multiple arc a sensitive galvanometer, and a 

 rarefied-air space, 5 mm. long, between aluminium 

 electrodes. The galvanometer is also shunted by a 

 wire; and one junction of this shunt with the rest of 

 the circuit is grounded. When the Holtz machine is 

 worlced, frequent sparks pass, and the galvanometer- 

 needle finally attains a nearly constant deflection. 

 The singular fact is observed, that this deflection is 

 many times greater, when the galvanometer is shunted 

 by the rarefied-air space, than when it is not so 

 shunted. The explanation proposed is, that, after 

 each sparii from the Holtz machine passes through 

 the rarefied-air space, a 'disjunction,' or reverse cur- 

 rent, is set up by the e. m. f., which the discharge has 

 generated at the surface of the electrodes. This cur- 

 rent passes through the galvanometer in the same 

 direction as the current from the machine. 



Edlund's articles seem to be of value in calling par- 

 ticular attention to the long-recognized resistance at 

 the surface of the electrodes in a discharge-tube, thus 

 making it appear probable that the proper resistance 

 of rarefied air has been overestimated, and so tend- 

 ing to remove the difiiculty at present felt in regard 

 to the height of auroras. Edlund's own conclusion 



— viz., that empty space, or rather the ether, is an ex- 

 cellent conductor^ will probably be accepted by few. 



— (Phil, mag., Ja.n.) E. H. H. [421 



ENGINEERING. 

 The Corinth canal. — As early as the year 625 

 B.C., the idea of connecting the gulfs of Corinth and 

 Aegina by means of a canal was conceived. It was 

 abandoned after some discussion, from the belief 

 that the level of the sea in the gulf of Corinth was 

 higher than that in the gulf of Athens. Later, Julius 

 Caesar, Caligula, and Nero employed engineers to 

 plan this work; but little was actually accomplished. 

 Quite recently Gen. Tiirr obtained a concession from 



the Hellenic government to cut a canal across the 

 isthmus, of dimensions sufficient to pass one vessel 

 at a time; the cross-section being the same as that 

 of the Suez Canal, i.e., 72 feet wide at the bottom, 

 and with a depth of 26 feet. Three several routes 

 were surveyedj being respectively 3.94 miles, 4.2 miles, 

 and 6.8 miles in length. The first of these lines was 

 selected, being the same as that proposed by Nero's 

 engineers. The work was commenced last May, the 

 estimated cost being thirty million francs. It is be- 

 lieved that the investment will be a good one, as the 

 traflic across the isthmus is now from five to six mil- 

 lion tons annually. — {Engineering, Dec. 8, 18S2. ) 

 G. L. V. [422 



The Kinzua viaduct. — This remarkable struc- 

 ture cai-ries a branch of the New- York, Lake-Erie, and 

 Western railroad, over a deep goi-ge in western Penn- 

 sylvania, the Kinzua Creek. This is the highest rail- 

 road-bridge in the world, the distance of the rails 

 above the stream being .301 feet, while the whole 

 length of the work is 2,(J52 feet. The structure is de- 

 signed to sustain a continuous line of the heaviest 

 locomotive engines from one end to the other, or 2,660 

 tons in all. The original conception of a viaduct at 

 this place is due to Mr. O. W. Barnes, C. E. The 

 execution has been made nuder the general direction 

 of Mr. O. Chanute ; the details being arranged and the 

 construction carried out by Messrs. Clarke, Reeves, 

 and Co. of Philadelphia. The total cost of this enor- 

 mous structure was but $237,000, and the time occu- 

 pied in building was only 94 days. The towers were 

 erected without scaffolding of any kind, while the 

 superstructure was placed in position by means of a 

 travelling crane; a method which secured economy 

 of both time and money. Especial care has been 

 taken to enable the structure to resist the severest 

 gales of wind. Ample provision, too, has been made 

 for the effect of heat and cold upon the iron-work. — 

 {Engineering, Dec. 22, 29, 1S82.} G. L. v. [423 



Centrifugal pumps. — The common objection to 

 this kind of pump is, that it wastes a large percentage 

 of the power applied; but G. Kapp of London main- 

 tains, that, if the pump is rightly made and rightly 

 worked, it will utilize as large a i^ercentage of the 

 applied work as any hydraulic machine. He gives 

 the mathematical theory of the centrifugal pump/ 

 shows how to find the loss through friction, investi- 

 gates the best form for the wheel-blades, and lays 

 down general rules for the construction throughout. 

 — ( Cimlingenieur, heft 4, 1882. ) g. a. h. [424 



CHEMISTRY. 



( General, physical, and inorganic.) 



Formation of natural manganese binoxide, 



and certain reactions of other peroxides. — 



From the results of M. Berthelot, it seems that the 

 heat of formation of Mn Oo in the reaction Mn O -h O 

 = Mn Oj is larger by 3.9 cal. than that of Mn C O3 in 

 the reaction CO2 (in solution) + Mn O = Mn C Oj. 

 An explanation is thus found for the formation of the 

 mineral pyrolusite by the action of air, either free, or 

 dissolved in water. In the reactions 2 Fe O -|- O = 

 Fe.203,-1-1.3.3 cal. for FeO; 3 Fe O -|- O = Fe,0,, + 

 10.3 cal. for FeO; CO. (in solution) -I- FeO=FeCO:j, 

 + 5 cal. (or, COo (gaseous),-!- 7.Scal.), — more heat is 

 evolved in the formation of the oxide than of the car- 

 bonate. The stability of Ba C O3 is shown in the 

 reactions Ba -|- O = Ba O, -f 6 cal. ; Ba O + C Oa = 

 BaCOj, -)-28 cal. Hydrogen peroxide cannot be 

 formed from MnO,, since there would be an absorp- 

 tion of heat: Mn 0? + H CI = MnCl, -f HjO., — 9.7 

 cal. It cannot be formed from ferric oxide, since the 

 quantity of heat absorbed would equal — 16 cal. With 



