340 



SCIENCE. 



[Vol. I., No, 12. 



Two experiments were tried. In the first, tlie yellow 

 light remained stationary, and the bine one was 

 moved towards the screen till equality of tire shadows 

 was obtained. In the second exj^eriraent, the blue 

 light was left in its first position, and the yellow one 

 moved away from the screen till the shadows were 

 equal. On comparing the results obtained, it was 

 found that they differed materially from one another. 

 In another experiment the two shadows were cast 

 so that when the eye was in a certain position they 

 appeared of equal brilliancy. On approaching the 

 screen, the blue shadow was found to appear more 

 brightly lighted than the other; and, on going away 

 from the screen, the reverse effect was observed. To 

 further investigate these results, two methods of 

 measurement were employed: 1. The intensity of 

 the light corresponding to the different wave-lengths 

 of the spectrum was determined by means of a Rum- 

 ford photometer, as above described ; 2. A small 

 figure consisting of three short, broad, black lines, 

 drawn on a white surface, was placed in different 

 portions of the spectrum, and the intensity of the 

 light increased or diminished until its outlines were 

 just distinguishable. 



It was found that the results obtained by the two 

 methods agreed almost exactly for the less refrangible 

 portion of the spectrum, as far as wave-length 517 ; 

 but beyond that point the differences suddenly be- 

 came very marked; and it was shown that a blue 

 light had to be many times brighter than a yellow 

 one in order to distinguish the same details by its 

 aid; also, that the brighter the lights were, the more 

 marked did this difference become. 



Now, for purposes of artificial lighting, whether 

 public or private, the end desired is less to produce a 

 luminous sensation upon the eyes than to enable us 

 to distinguish the objects around us. It is there- 

 fore concluded, that,' for lights of equal brilliancy, 

 the superiority of yellow sources (such as gas-flames 

 and incandescent electric lamps) to sources richer in 

 the blue rays, as the arc light, is beyond question. — 

 (Journ. x)hys.,'S'eb.) w. H. p. [696 



Electricity. 

 Transmission of power. — Experiments relating 

 to the electrical transmission of power were made 

 on the 4th of March last, in Paris, at the Chemin de 

 fer du Nord, before a commission of the French 

 institute, composed of MM. Bertrand, Cornu, Tresca, 

 de Lesseps, and de Freycinet. The j-esistance of the 

 line was 160 ohms, — a resistance equivalent to that 

 offered by a copper wire 106 kilometres in length, and 

 4 mm. in cross-section. The power applied to the 

 generating-machine was equivalent to 4.4 horse- 

 power ; and the rotation of the generating armature 

 was varied from 380 to 1,024 revolutions per minute 

 in order to ascertain the effect of speed of rotation 

 upon the mechanical return at the other end of the 

 line. As the general result of the experiments, ' La 

 Lumiere electrique ' announces that the available 

 power transmitted was 47.5% of that which actu- 

 ated the generating-machine. — {La Lum. electr., 

 March 17.) a. g. b. [697 



ENGINEERING. 

 Steel for structures. — Mr. Ewing Matheson dis- 

 cusses at considerable length the important question 

 of the modern use of steel for engineering-works. 

 The author commences by stating the following prop- 

 ositions: 1. Rolled plates and bars of the various 

 forms required for structures are now made of steel 

 with as much certainty, in regard to quality, as iron 

 of the first class; 2. Advantages in regard to size 



and weight of pieces can be obtained in steel, which 

 in iron are either impossible, or can only be had at 

 very great expense; 3. Steel has a superiority in 

 strength, ranging from once and a half to twice that 

 of iron, and at the same time a more than proportion- 

 ate superiority in ductility and elasticity; 4. Steel 

 can be bent, straightened, cut, punched, planed, and 

 drilled with the same tools and processes that are 

 used for iron, and, for the most part, without extra 

 force; 5. Protection against rust is of more impor- 

 tance for steel than for iron, but, if treated in the 

 same way as is usual with iron, steel is less liable to 

 waste by rust; 6. Owing to the above advantages, 

 structures of steel are superior to those of iron, but 

 economically it is only in some cases in regard to 

 ships, and in still fewer cases in regard to bridges, 

 that there is at present any pecuniary advantage in 

 using steel ; 7. This limit to the application of steel 

 is due partly to official rules, which restrict the work- 

 ing-strains on steel, and partly to exigencies of de- 

 sign, which hinder the reduction in size and weight of 

 members to the extent which its superior strength 

 might otherwise allow; 8. Although, for the above 

 reasons, steel structures may cost more than iron 

 without any immediate compensation, yet, if meas- 

 ured by actual units of strength and durability, steel 

 is cheaper as well as better for all but very small struc- 

 tures; 0. The employment of steel may be encour- 

 aged and extended by a fuller knowledge, among those 

 who use it, of its qualities, by facilities for verifying 

 these qualities by exercising a wider choice of the 

 kind of steel suited to the purpose in view, and by 

 such a liberal alteration of the present official rules 

 as will allow fuller advantage to be taken of steel than 

 is usual or permitted at present. The simplicity of 

 manufacture, as compared with that of rolled iron, 

 renders almost certain a nearer approximation in cost, 

 if, by a wider permission, the demand for steel should 

 increase. Each of the above points is taken uxi in de- 

 tail and carefully considered, the admiralty specifica- 

 tions for steel plates for ships are given, the question 

 of steel riveting is examined, the important matter 

 of rust is discussed, and an extended comparison is 

 made between theweiglit and cost of iron and steel 

 for bridges. The whole paper is of great value, and 

 well worth careful study. — {Proc. inst. civ. eng.) 

 G. L. V. [698 



Recent hydraulic experiments. — At a meeting 

 of the Institution of civil engineers held in London 

 Nov. 14, 1882, Major Allan Cunningham gave an 

 account of an extensive course of experiments on the 

 flow of water in the Ganges canal, extending over 

 four years (1874-1879), the principal object being to 

 find a good mode of discharge measurement for large 

 canals, and to test existing formulae. Not less than 

 fifty thousand measurements for velocity were made, 

 and six hundred for surface slope, while five hundred 

 and eighty-one cubic discharges were measured under 

 very varied conditions. Forty measurements of evap- 

 oi'ation from the canal surface were made in a floating 

 pan, during twenty-five months. The results showed 

 the movement of water in such a canal to be in many 

 respects quite different from those before reported. 

 — {Enrjineering, 'Nov. n,lSS2.) Q. L. v. [699 



Railroad accidents, and the earth's rotation. — 

 R. Randolph shows tliat the deflective force arising 

 from the earth's rotation is entirely too small to de- 

 termine derailments, and also, that, as an excess of 

 right-handed derailments has been credited solely to 

 north and south tracks, this proves it to be wholly im- 

 aginary ; for the deflective force at any latitude is the 

 same for all directions ( Van Nostrand's engin. mag., 

 1883, 117). The numerical results given are but half 



