512 



NATURE 



[August 23, 19 17 



of this country on a secure foundation, a task in which 

 the Optical Society, where manufacturers and scientific 

 workers are brought into intimate contact with one 

 another, is eminently fitted to lead. 



The most recent contribution of the Bureau of 

 Standards to the problem of the photometry of sources 

 of light of different colours is Scientific Paper 

 No. 299, by Messrs. Crittenden and Richtmyer, who 

 have arrived at a number of general conclusions by 

 collating the measurements made by more than a 

 hundred observers. When two light sources of dif- 

 ferent colours, such as a carbon and a tungsten 

 filament lamp, are compared by a photometer de- 

 pending on a setting for equality of brightness, a 

 considerable amount of practice is necessary before 

 consistent results are obtained by any observer not 

 specially trained. When a flicker photometer is used 

 an observer of fair ability can readily get good 

 results, but they differ from those given by the 

 former method. The flicker photometer may give, 

 e.g., the candle-power of a tungsten lamp 3 per cent, 

 less as compared with a carbon lamp than does an 

 ordinary photometer. If the colour sensation of the 

 observer differs from the normal, his comparison 

 differs in consequence, but the authors find that the 

 Ives-Kingsbury method of standardising the eye by 

 the use of glass cells containing aqueous solutions of 

 potassium bichromate 72 grams, and copper sulphate 

 crystals 53 grams, to the litre respectively, interposed 

 between the photometer and two equal sources of 

 light, enables such an observer to get results identical 

 with those obtained with a normal eye. 



The extent to which viscometers of various forms 

 are now used for the classification and identification 

 of oils and other liquids has led the Bureau of 

 Standards to take up the question of a supply of 

 standard liquids of known viscosities for the standard- 

 isation of viscometers. The investigation of the most 

 suitable liquids has been carried out by Messrs. E. C. 

 Bingham and R. F. Jackson, of the Bureau, who con- 

 clude that mixtures of 20, 40, and 60 per cent, by weight 

 of ethyl alcohol in water, and solutions of sucrose in 

 water containing 20, 40, or 60 per cent, by weight of 

 sucrose, form the most suitable standard liquids. They 

 give the viscosities and fluidities of these liquids at 

 temperatures from 0° C. to 100° C. at intervals of 

 10° C. in a series of tables, and the variations of the 

 fluidities with change of concentration and tempera- 

 ture are shown by a series of curves. The simple 

 shapes of these curves suggest that it would be better 

 to use the fluidity rather than its reciprocal the vis- 

 cosity, in all calculations on the subject. 



The Tasmanian Government's Great Lake hydro- 

 electric power undertaking, inaugurated in 1909 and 

 opened last year, is described in the issue of the 

 Engineer for July 2:7. It is based chiefly on a joint 

 utilisation of twc rivers— the Ouse and the Shannon — 

 the latter having its source in the Great Lake and 

 the former in what are known as the Ninety-nine 

 Lagoons. The Great Lake lies at a level of 3250 ft. 

 above the sea, and the lagoons are seme 200 ft. higher. 

 A curious feature of the two rivers is the great dis- 

 similarity of their gradients, in spite of the fact that 

 their sources are but a few miles apart, and their 

 junction merely twenty miles or so downstream. At 

 one point, about five miles south of the Great Lake, 

 the Ouse is actually 1300 ft. below the Shannon. A 

 dam has been built across the south end of the lake, 

 giving an additional depth of 11. ft., and increasing the 

 storage area from forty-two to fifty square miles. The 

 catchment basin lies in the centre of the island, and is 

 some 227 square miles in extent, and the annual pre- 



NO. 2495, VOL. 99] 



cipitation of rain and snow is upwards of 60 in. By 



means of a diversion weir the water from the Shannon 



is turned into a canal, which serves a storage reservoir 



of 380 acres The power station is on the banks of 



the Ouse, and this river receives the exhaust water. 



The difference in level from reservoir to power station 



gives a net head of 1015 ft. of water, sufficient to 



develop a normal output of 4900 brake-horse-power in 



each of two turbines already installed. The installa- 



: tion has, in fact, proved so successful that an extension 



; is now in hand. Although at present only serving the 



town of Hobart, the central position of the station 



renders it convenient for the transmission of power to 



I any point in the island. 



I Messrs. Bernard Quaritch, Ltd., ii Grafton Street, 

 \ W.I, have issued a useful catalogue (No. 349) of rare 

 I and valuable bocks, comprising, among others, works 

 dealing with Africa, America, Australia, entomology, 

 ; ornithology, and physical and natural science. The same 

 ! firm has purchased the existing stock of " Biologia 

 I Centrali-Americana," and has in preparation a detailed 

 I prospectus of the work. 



OVR ASTRONOMICAL COLUMN. 



The Commencement of the Astronomical Day. — 

 In a letter to the Observatory for August the As- 

 tronomer Royal and Prof. H. H. Turner invite ex- 

 pressions of opinion from astronomers as to the 

 desirability of adopting the civil day — i.e. the day 

 commencing at midnight — in astronomical ephemer- 

 ides ; and, if thought desirable, as to the most suit- 

 able date for introducing the change. It has usually 

 been considered convenient that observations made 

 during the same night should all be of the same date, 

 but this does not seem to them to balance the ob- 

 jection of having a time at variance with the civil 

 reckoning. It is pointed out that the arrangement 

 I which is convenient for observations of stars is in- 

 I convenient for observations of the sun, and that the 

 ! change would probably be welcomed by navigators. 

 I Ihe only serious difficulty seems to be the discon- 

 I tinuity which would thus be introduced into astro- 

 ' nomical records. A change of this kind could only 

 come into operation after some time, as the national 

 I ephemerides are prepared several vears in advance. 



Observations of Mira Ceti. — In Ast. Nach., 4892, 

 I Prof. Nijland gives particulars of seventy-nine obser- 

 I vations of Mira made at Utrecht between July 20, 

 1916, and February 15, 1917. The most probable 

 date of minimum was July 24, when the star was of 

 magnitude 94. The maximum occurred on Novem- 

 ber 8 (J. D. 2421176), the magnitude then being 375. 

 The following is a summary of recent maxima ob- 

 served by Prof. Nijland, together with a comparison 

 with Guthnick's ephemeris : — 



Maximum Guthnick Ob^.-G. Mag. Period 



J. D. 2420199 0209 — lod 335 



0527 0^39 —12 3-8 



0852 087.5 -18 3-5 



1 176 1201 -25 3-75 



328d 

 325 



324 



Eclipsing Variables. — A further important contri- 

 bution to the study of eclipsing variables has been 

 made by Prof. H. N. Russell in collaboration with 

 Mary Fowler and Martha C. Borton (Astrophysical 

 Journal, vol. xlv., p. 306). The observational data 

 were provided by the Harvard Observatory in 

 the form of 2101 observations of the photo- 

 graphic brightness of the six eclipsing variables, 

 W Delphini, U Sagittae, S Cancri, RW Tauri, SW 

 Cygni, and W Ursae Majoris. The resulting light- 



