TRANSACTIONS OF THE SECTIONS. 25 



On the morning of the transit the preparations were all complete, and every 

 assistance was rendered to the astronomers by Captain Fairfax and Captain Inglia 

 and the other officers. At Stations 2 and 3 excellent results were obtained at 

 ingress ; but a cloud prevented internal contact being obtained at Station 1. During 

 the progress of the transit a few photographs, and some measures with the double- 

 image micrometer, were taken at Station 1, clouds, however, interfering with con- 

 tinuous work. At egress both internal and external contact were observed at 

 Stations 1 and 3. 



Considering the position of the Island of Desolation, these results were considered 

 satisfactory, and the determination of the longitude was pursued with all possible 

 energy. A most successful chronometer-run had been made from the Cape of Good 

 Hope under the direction of Lieut. C. Corbet, R.N., who also connected the three 

 British Stations in Kerguelen with those of America and Germany ; but as the 

 longitude must depend mainly on lunar observations, no opportunity was lost of 

 observing the moon. An altazimuth, especially designed by Sir G. B. Airy for 

 Kerguelen, procured for the longitude ninety double observations of the moon's 

 azimuth or zenith-distance ; whilst the transit gave nineteen meridian passages of 

 the moon, and the equatorial one occultation. 



In the mean time the observers carried on a very complete series of meteorological 

 and magnetic observations, which were continued during the homeward journey, 

 and the Rev. A. E. Eaton studied the natural history of tue island. 



Goats and rabbits were left on the island to propagate. 



On February 26th the lunar observations were considered sufficient to secure a 

 fundamental longitude ; and, provisions running short, in less than two hom-s after 

 the last meridian observation of the moon H.M.S. ' Volage ' and ' Supply' were on 

 their way, one to Ceylon, the other to the Cape. 



About a week after leaving the Island of Desolation H.M.S. 'Volage' encountered 

 a cyclone, which might have ended unfortunately for the observers, though their 

 observations were secured by being sent home in duplicate on board H.M.S. 

 'Supply' and the 'Monongahela,' U.S.N. 



The other Government Expeditions were sent to the Sandwich Islands, to New 

 Zealand, Egypt, and Rodriguez ; and all were successfid except New Zealand, where 

 only a few micrometric measm-es were obtained. 



The Stations in India and Australia, Lord Lindsay at Mauritius, and other 

 private observers were also fairly fortunate ; so that we may hope that England will 

 aid largely towards the accurate determination of the solar parallax. 



Light, Heat, and Electricity. 



On the Ratio of the Actinic Poiver to the Illuminating Poiver of the Magneto- 

 Electric Light. By Capt. W. de W. Abnet, B.E., F.O.S., F.B.A.S. 



In some recent experiments with magneto-electric machines driven at varying 

 speeds, and consequently with varying engine-power, the author obtained photo- 

 metric measurements, by optical and also photographic means, of the dift'erent 

 intensities of the light produced. 



At iii'st sight a discrepancy seemed to arise between the resiilts obtained from 

 the two distinct methods. When, however, the values were laid down graphically, 

 showing the power of the lights in comparison with the work expended in their 

 production, the resulting cm-ves became interesting ; they showed that the actinic 

 power of the light diminished much more rapidly than the optical power as the 

 " work done " decreased. 



The results of the experiments also showed that there is a certain point for each 

 machine beyond which it is wasteful to increase the motive power, the increase in 

 optical or actinic value of the light being very small. 



1875. 



