PHYSICS, PROGRESS OP', IN 1891. 





tin at and eyes that have communicated signifi- 

 cant data. Some recent pictures of (hi- lurvnx 

 an- \aliial>ly complete. The image is si-cured l>y 

 tlic aid of electric illiiiniiiatioii. From the 

 physiological laboratories arc reported efforts ti 

 secure photographic, rccnrds <.f nervous and 

 muscular action. In tho preservation of patho- 

 logical records in general the caiucni is of great 

 utility. 1'hoto-microscopy is in extensive opera- 

 tion in many of the sciences. Mining, mineralogy, 

 surveying, and exploration all utilize photo- 

 graphic aid. Tin- photographic corps has be- 

 come an essential element of tho modern army, 

 occupying close relations with the balloon service. 

 Historical events of every description are now 

 photographed in <:rtt'>iao. Societies of amateurs, 

 in some recent instances, have secured the co- 

 operation of civil authorities in enabling them 

 to record all events necessary to the complctc- 

 ne>s of local historical records. 



Photo-mechanical Processes. The revolu- 

 tion in the reproductive arts is one of the re- 

 sults of photographic advancement. Newspaper, 

 magazine, and book illustration have wholly 

 changed in character. . There is much com- 

 petition in the effort to secure a "half-tone" 

 plate direct from the photograph, which may In- 

 convenient ly printed with type. There hns been 

 a rapid advance in this method, which is largely 

 used in illustration of all classes. Hut in print- 

 ing qualities no half-tone nlato mechanically 

 produced has yet equaled tne engraved block, 

 being deficient in depth and in the modifications 

 of --iirface which the engraver can impart. The 

 faithfulness of tho photo-mechanical plate, how- 

 ever, is beginning to be widely prized among 

 artists, who formerly resented any agency but 

 thai of engraving, but who now find the im- 

 proved " process " plate to be possessed of dis- 

 tinct advantages over any but the best en- 

 graving. Other photogravure processes have 

 reached a high state, of perfection, permitting 

 the printing from plates having all the char- 

 acteristics of the original photographic plate. 

 (it-latin is playing a prominent part in most of 

 these methods. Several processes use the surface 

 of the negative itself, utilizing the hint offered 

 by the species of relief produced in photo- 

 graphic action. 



PHYSICS. PROGRESS OF, IN 1891. 

 Constitution of Matter. The Xther.Prot. 

 Nipher, in an address before the physical section 

 of the American Association for the Advance- 

 ment of Science (1891), gives a comprehensive 

 review of tho history of this subject. Prof. 

 I.odire. in a British A-socjatiou address, describes 

 his experiments on the disturbance of the ether 

 in the neighborhood of a rapidly moving body. 

 A rag') found no such disturbance, and Lodge's 

 experiments, conducted on a different line, con- 

 firm this result. He caused light to fall on a 

 feebly silvered glass plate, so that part was 

 transmitted and part reflected. The rays thus 

 separated were caused to pa-s in opposite direc- 

 tions between two coaxial steel disks, and then 

 made to interfere. The effect was the same 

 whether the disk's were still or rotating rapidly. 

 T. Whitcher (" Electrician.'' May S) suggests that 

 many difficulties in our conception of the ether 

 are removed if we regard it not as pas-ivc and 

 acted on by external forces, but as a continually 



agitated source of energy. He conclude* that 



the most agitated ether is the Ix-st iii-ulu' 

 energy, and the quietest is the i ^. r> 



MuJiTiilur l)iHt(irirrn. P. Jacobin (I 

 ems of Science-. Jan. 1'Ji concludes that all tin- 

 physical properties of metals of the mrm- group 

 depend exclusively on molecular distance. J-'or 

 instance, for ordinary metals clcciric conduc- 

 tivity is proportional 'to the M\th power of the 

 number of molecules in a given volume; for 

 magnetic metals it is h, \er-dy as the sixth 

 power of their distance apart. 



Mechanics, (ininty. Prof. .1. H. I'oynting 

 (London Royal Society. June 4) has BMMmw 

 the earth's density and the gravitation CM 

 by a common balance having a beam 123 centi- 

 metres long. Two spheres of lead or antimony. 

 weighing21 kilogrammes each, were so suspended 

 from the arms that their centers were about :i(i 

 centimetres above the center of a mass of the same 

 metal weighing 153 kilogrammes. This mass, 

 being placed on a turn-table, could be shi! 

 as to 1 e directly under citherarmof the balance. 

 With the aid of very delicate adjustment 

 careful precautions the gravitation constant was 



i?./*{i*J A 



found to be - and the earth's mean density 

 1U 8 



5-4934. 



Specific Gravity. W. J. Sollas ("Nature." 

 Feb. 20) finds the specific gravity of any minute 

 object, such as a butterfly's wing-scale or a drop 

 of blood, by means of a glass tube filled with u 

 heavy fluid diluted with another which does not 

 perfectly mix with it. After standing, the 

 mixed fluid is found to increase continuously in 

 density from above downward, and therefore 

 specks placed in it show their specific gravity by 

 the level at which they float. The instrument 

 is graduated by small floating fragments of 

 mica or minute glass bubbles. 



Hardness. Prof. Auerbach. of Jena (" Rcper- 

 torium fur Physik"), measures the hardness of a 

 transparent body by pressing upward against a 

 plate of it the spherical surface of a lens by 

 means of a weighted lever. The effect is ob- 

 served microscopically. He finds that hardness 

 increases with elasticity, but less rapidly. 



I-'li.ntrt'. ('. A. Cams-Wilson, (London Phys- 

 ical Society, June 2(t) has studied the flexure'of 

 glass beams by means of the jxilarix-ope. The 

 strains thus observed in a loaded beam differ 

 from those usually assumed. The "neutral 

 axis." instead of coinciding with the axis of the 

 beam, is raised in the center, and its shape de- 

 pends on the load and the span. 



Impact Prof. P. G. Tait (Edinburgh Roval 

 Society. Jan. fi) finds that solids can be divided 

 into two cla-scs. in one of which the duration of 

 impact remains constant, whatever the distortion, 

 up to a certain limit ; beyond this the duration 

 is shorter as the distortion increases. In tin- 

 other class 1 1. e du nit ion first increases with the 

 distortion, then becomes constant, and finally 

 diminishes. Vulcanized, caoutchouc is a tyj>e of 

 the former class, cork of the latter. 



Jf/tifi<ni.K. Prytz ("Annalcn der Physik 

 uud Chemie" vii. 181)1) measures the time of 

 rapid rotation by means <.f a falling b<>< 

 which the rotating body spurts a tine jet of 

 coloring matter, thus avoiding the fricticn.-d 

 retardation of the tuning-fork method. H 



