490 



NATURE 



[December 30, 1915 



Monitor, and a large number of volumes dealing with 

 the South African war of 1899-1902. The catalogue 

 also includes more than sixty oil paintings by James 

 Baines, who had a wide experience of southern tropical 

 Africa, and was with Livingstone on his Zambezi ex- 

 pedition. The only other known collections of Baines's 

 pictures are in the possession of the Royal Geograph- 

 ical Society and the museum at Kew Gardens. The 

 catalogue is exclusive of Mediterranean Africa and the 

 Red Sea border. 



OUR ASTRONOMICAL COLUMN. 

 Sun-spots and Pressure. — A paper dealing with 

 pressure data has been received from Dr. Gilbert S. 

 Walker, who is engaged on a comprehensive statistical 

 investigation in world meteorology with the object of 

 laying the foundation of a secure system of seasonal 

 weather forecasting. The data are treated as in the 

 case of rainfall and temperature in preceding papers. 

 For pressure the Indian area is characterised by nega- 

 tive correlation coefficients, whilst in the western hemi- 

 sphere and boreal regions the opposite sign prevails. 

 A general tendency is observable for the pressure co- 

 eflficients to be opposite in sign to those for rainfall, 

 indicating that their variations are dominated by a 

 common cause, and temperature would seem to have 

 little influence on either. Humidity, especiallv in the 

 upper air, appears to control the relationship between 

 sun-spots and temperature (Mem. Indian Met. Dept., 

 vol. xxi., part xii., No. vi.). 



Harmonic Analysis of the Motions of the Helium 

 Stars. — The dynamics of our stellar system are engag- 

 ing an increasing degree of attention, and although 

 Alcyone, and, recently, Canopus have been the sug- 

 gested super-suns, it is still a question of establishing 

 the existence of the general orbital movement. 

 Prof, von S. Oppenheim adopts the working hypothesis 

 that such movement exists, and some results of his 

 work in this field were recently noted in this column 

 (October 21). In an earlier investigation Prof. Oppen- 

 heim employed harmonic analysis to answer cognate 

 questions. This is now recalled because these investi- 

 gations have lately been carried a stage further (Astro- 

 nomische Nachrichten, 4822). Pursuing the analogy 

 drawn from the swarm of minor planets, he observes 

 that a precise parallelism probably exists if instead of 

 dealing with the totality of the stars the movements of 

 the galaxy-grouping helium stars (type B) are alone 

 taken into account. Employing the methods of the 

 earlier papers to deal with the Lick results for the 

 radial velocities of 233 stars of this type, taking proper 

 motions from the Boss Catalogue, and making an 

 approximation in regard to parallax, he finally obtains 

 as developments of expressions involving respectively 

 proper motions and radial velocities two Fourier series 

 the terms of which are in good agreement regarding 

 an orbital position angle of the sun, a result considered 

 to establish the reality of the original hypothesis (i.e. 

 that the stars, including the sun, move in circular 

 orbits about one ideal centre). The numerical results 

 which may be specially mentioned concern the position 

 of this centre. Taking ^=234° 40' as the ascending 

 node of the plane of the sun's way, with inclination 

 » = 53°. then the sun viewed from the centre of the 

 system appears in R.A. 203° 55', declination -34° q'. 

 The corresponding apex of the solar motion is R.A. 

 266°, and declination +34° 37'. 



The Astronomical and Astrofhysical Society of 

 America. ^ — We have received a copy of the second 

 NO. 2409, VOL. 96] 



volume of the publications of this peripatetic society. 

 The meetings reported range from the eleventh, 19 10 

 — attended by a number of important English astro- 

 nomers — to the fifteenth, 19 13. Abstracts are given of 

 the papers. A most important feature of the volume 

 is an appendix devoted to Halley's comet. The special 

 committee of the Astronomical Society made sugges- 

 tions that led to Mr. Ferdinand Ellerman taking an 

 expedition to Honolulu to secure a record of the 

 appearances presented by the comet during the spring 

 of 1910. Two cameras were employed, a 6-in. 

 Brashear, f.l. 31-8 in., and a Bausch and Lomb Tessar 

 lens of 57 mm. aperture, and 251 mm. f.l. The 

 greatest length of tail photographed with the latter 

 was 50° on May 14. The photographs obtained are 

 described by Prof. E. E. Barnard, and no fewer than 

 forty-seven are reproduced. The dates range from 

 April 26-June 6. The Comet Committee also publish a 

 very extensive index catalogue of photographs of the 

 comet, giving date, time of exposure, optical constants, 

 place, and an indication of the technical quality of the 

 photograph. 



T' 



PROBLEMS OF EFFICIENT METHODS OF 

 DOMESTIC HEATING. 

 HE determination of the efficiencies of different 

 methods of heating is a problem very difficult 

 to solve on a purely scientific basis. It is, indeed, 

 difficult to attach a precise meaning to the expression 

 " efficiency " in connection with heating apparatus. 

 I The word as commonly understood in connection with 

 devices for the utilisation of energy in any form means 

 the ratio of the total amount of energy utilised to that 

 consumed. In a heating apparatus it is difficult to say 

 what fraction of the energy is to be regarded as 

 "utilised." If we regard that heat only as utilised 

 which is delivered into the air of a room, in one sense 

 every apparatus which when suitably disposed delivers 

 almost the whole of its heat into the air of a room may be 

 regarded as having nearly the maximum possible 

 efficiency — 100 per cent. Such, for example, is the 

 electric low-temperature stove (not taking into account 

 the generating mechanism or boilers from which the 

 heat is ultimately derived), or the oil stove, or the gas 

 radiator, which deliver the products of combustion 

 into the air of the room. 



But heat is delivered into a room not only by con- 

 vection currents of heated air, but also by the con- 

 version of radiant energy into heat. The proportion of 

 the radiant energy which may be converted into heat 

 is essentially uncertain. It depends on the position 

 of the radiant body relatively to the windows, walls, 

 furniture, etc., and on other circumstances. If there- 

 fore the "efficiency" of the apparatus depends on 

 such extraneous considerations, it is evidently out of 

 place to use, in connection with this matter, such a 

 word as "efficiency," which has a precisely defined 

 significance. Alternatively we are debarred from re- 

 garding the air heat as the only "utilised" energy. 



Functionally, a heating apparatus is one by which 

 a certain amount of heat energy is passed through a 

 room to the outer air. As a consequence of Its 

 passage, certain thermal and other conditions in the 

 room are maintained. If the resistance interposed 

 between the room and the outer air Is relatively high, 

 the same flow of heat will maintain a higher tem- 

 perature than if the resistance is low. In the limit 

 if the resistance were supposed infinitely great, the 

 thermal conditions might be conceived to be main- 

 tained without any expenditure of heat whatever. It 



