126 



S CIENCE- GOSSIP. 



CONDUCTED BY JAMES QUICK. 



Newton and Optics. — The Rede lecture upon 

 "The Wave Theory of Light," was delivered at 

 Cambridge in July by Professor A. Cornu, on the 

 occasion of the jubilee celebration of Sir G. Stokes as 

 Lucasian professor. The French savant sketched in 

 an absorbing and brilliant manner the history of the 

 theories of Light from the ancients, down through 

 Boyle, Descartes, Newton, Young, and Fresnel, to 

 our present physicists. He naturally laid stress upon 

 the thoughts of Sir Isaac Newton and Augustin 

 Fresnel as foremost workers of their time. Professor 

 Cornu dilated upon the troubled mind of the former 

 in endeavouring to apply at one time the emission 

 theory, then the theory of fits, then again the un- 

 dulatory theory to the elucidation of optical problems. 

 Indeed, Thos. Young cites some of Newton's 

 " Queries " as proof of the final conversion of Newton 

 to the wave theory. Although it is to Thos. Young 

 we owe the discovery in 1S01 of the true wave nature 

 of light, yet it was the illustrous Fresnel who so 

 vigorously pursued it, and to his investigations it is in 

 a great measure due that the wave theory of Light 

 was so firmly established. 



Photography at Low Temperatures. — 

 According to MM. Lumiere, a great decrease in the 

 sensitiveness of photographic plates takes place at low 

 temperatures. Their experiments show that some, 

 ultra-sensitive photo-plates cooled to — 191" C 

 require from 350 to 400 times as long an exposure to 

 light to produce a given effect, as is taken at ordinary 

 temperatures. Most sensitive photographic prepara- 

 tions are not acted upon at all under such cold 

 conditions. The plates, however, are not per- 

 manently affected by the cooling. 



Fluorescent Solid Solutions. — In an interest- 

 contribution to " Comptes Rendus" 128, J. R. 

 Mourelo gives the results of his experiments upon 

 fluorescent substances. Taking various mixtures, he 

 finds that the best results are obtained with strontium 

 carbonate 100 grams, flowers of sulphur 33 grams, 

 sodium carbonate I '4 gram, fused sodium chloride 

 0"85 gram, manganese carbonate o"l5 gram. This 

 mixture is finely powdered, compressed, and placed in 

 an earthenware crucible. It is kept at a red heat for 

 three hours and then allowed to cool slowly. If it is 

 then exposed to daylight it shows a brilliant green 

 fluorescence. 



Measurement of Thermal Conductivity. — 

 Further experiments have been made to determine 

 the thermal conductivity of various substances. An 

 arrangement used recently by Dr. C. H. Lees con- 

 sisted of a disc of the material whose conductivity was 

 to be determined, having a copper disc placed upon 

 one face, while upon the other were applied 

 a pair of copper discs, having between them an 

 electrical heating coil of platinoid wire. The discs 

 were all the same diameter. Radial holes were bored 

 into each copper disc and thermo-junctions inserted, 

 so that the differences of temperature could be 

 measured by balancing the differences of potential 

 produced, against known potential differences on 



a potentiometer. Dr. Lees summarised some 

 of his results as follows: — I. Solids, which are 

 not very good conductors of heat, in general decrease 

 in conductivity with increase of temperature in 

 the neighbourhood of 40^ C. Glass is an 

 exception to this rule. 2. Liquids, in the neigh- 

 bourhood of 30 C. follow the same law. 3. The 

 conductivity of a substance does not invariably change 

 abruptly at the melting point. 



Contact Break for Induction Coils. — The 

 spring contact break is now generally regarded as 

 quite unsuitable for large induction coils, having given 

 place to mercury breaks and more recently to the 

 Wehnelt electrolytic break {vide S.-G., May, 1899, 

 p. 372). For coils giving up to about 3m. or 4in. 

 sparks, however, the spring break may be advan- 

 tageously used. A modified form has recently been 

 introduced having two contacts instead of one, so that 

 as the spring vibrates it closes and opens the circuit 

 twice during each complete oscillation. The frequency 

 of break is thus doubled for the same period of 

 vibration of the spring. 



Electroplating the Hulls of Vessels. — A 

 satisfactory report has recently been submitted to the 

 United States Government upon a four years' test of 

 Crane's system of copperplating the hulls of vessels. 

 The ocean tug "Assistance" was electroplated, and 

 launched in February, 1895. Quite recently she was 

 docked and subjected to a critical examination, when 

 it was found that her bottom was absolutely free from 

 marine growth of any kind. Flexible shallow baths 

 are used in the process in order to conform to the 

 curvature of the ship. These baths, with suitable 

 watertight packing, are fixed to the sides of the ship 

 like snails. The ship forms the negative pole, the 

 plating .bath the positive, and the plating is done in 

 overlapping sections so as to form a continuous 

 coating. It is thus possible to plate the bottom of a 

 * ship 400ft. long in eight or nine days. The electricians 

 suggest in their report that not less than one-sixteenth 

 of an inch of copper should be allowed. It is claimed 

 that as much as ^4,000 per annum is expended by 

 various ships in the trans- Atlantic trade to overcome 

 the added friction caused by fouling, while the cost of 

 docking a big vessel twice a year, would nearly double 

 the total loss as a penalty for unprotected bottoms. 

 An iron vessel with a speed of 20 knots, if coated with 

 copper, will have, it is calculated, a speed of 21 

 knots. 



Glass and Porcelain Insulators. — Up to the 

 present time porcelain insulators have been most 

 generally used for telegraph and telephone work on 

 account of the hygroscopic nature of glass. Recently, 

 however, insulators have been made of a coarse kind 

 of glass, its composition being a trade secret, which 

 do not condense any film of moisture on their surface. 

 Experiments with these appear to show conclusively, 

 that they are much superior to porcelain. 



Printing by Rontgen Rays. — A process, known 

 as the Izambard process, has been brought forward for 

 printing by X-rays. A number of sheets of sensitized 

 paper are piled one on the top of the other, and 

 between the pile and the source of X-rays is placed 

 the copy, printed or written in ink made in part of 

 finely divided metallic or calcareous powder. Bronze, 

 copper, or white lead may be used. For a writing ink, 

 white lead in a solution of gum ; for a type-writing 

 ink, metallic powder mixed with boiled linseed oil. 

 An improvement recently made upon the Izambard 

 process consists in making the paper in a continuous 

 strip, and sensitizing it in page sections alternately on 

 opposite sides, in such a way that, when folded, each 

 section will still retain the features of a single sheet. 



