tkansactiojVS of section a. 551 



Captain Abney, Lewis Swift, Trouvelot, Dr. Max Wolf, Mendenhall, Mr. Christie, 

 the English Astronomer Royal, and Commodore Franklin, who wrote these words 

 from the United States Naval Observatory, Washington : — ' It seems to be 

 eminently proper that the nation which called the conference should be among 

 the first to adopt its recommendations.' The large shipping firm, Lloyds, are much 

 in favour of unification, 



(8) If shipping interests, upon which the Empire so much depends, desire 

 unification, the nautical astronomers, even though not a unit, should be asked to 

 accommodate their practice to suit navigators. The nautical astronomer was 

 made for the navigator, and not the navigator for him. 



(9) It is therefore hoped that the British Association for the Advancement of 

 Science will lend its aid in bringing this subject before the nations of the world for 

 final consideration. 



4. Preliminary Note on PJiotoyraphic Records of Objective Combination 

 Tones. By A. W. Rucker, F.R.S., R. W. Forsyth, and R. Sowter. 



The method of detecting the combination tones by the resonance of a fork was 

 the same as that used by Rilcker and Edser ^' Phil. Mag.' 39, p. 341, 1895). The 

 interference bands were thrown upon an opaque screen pierced with a narrow slit, 

 behind which was a revolving cylinder covered with photographic paper. When 

 the bands were undisturbed, the traces were parallel straight lines, but these 

 became wavy when the fork was set in vibration. All the principal results 

 obtained by Riicker and Edser were confirmed, and some new experiments were 

 made with Konig's wave-siren. 



FBI BAT, AUGUST 20. 

 The following Papers were read : — 



1. On the Determination of the Surface Tension of Water, and of certain 

 Dilute Aqueous Solutions by means of the Method of Rijyples.^ By 

 N. Ernest Dorsey, Ph.D. 



The method employed is a development of that used by Lord Rayleigh. But 

 by mounting the mirrors on arms rigidly attached to the carriage of a dividing 

 engine, and by viewing the light reflected from the surface of the liquid with a 

 telescope moimted on the carriage and provided with a spider line, 1 have succeeded 

 in measuring the length of the waves directly with the dividing engine, and with 

 considerable accuracy. 



By means of a small lens the horizontal beam of light is rendered parallel 

 before reflection from either mirror. The surface of the liquid was cleaned by 

 means of a flexible brass hoop, as in Lord Rayleigh's work. In reducing the results 

 I have used Lord Kelvin's complete formula. 



In a series of twenty-one determinations of the surface tension of water the 

 average was 73-24 dynes per centimetre at 18° C, or 75-98 dynes per centimetre at 

 0" C. ; and the average departure of a single result from the mean of the entire 

 series was only one-fifth of 1 per cent. This value diflers from the one found by 

 Lord Rayleigh by about 1 per cent., which is his estimate of the accuracy of his 

 determination, and it agrees with the value found by an entirely diflerent method by 

 M. Sentis in February of this year. 



The concentration of the solutions was varied from one-tenth normal to normal, but 

 most of the work was on solutions more dilute than one-half normal, and hence these 

 results are not strictly comparable with those obtained by others who have worked 

 on solutions not so dilute ; but, on the whole, the values here found are in accord 



' Published in the Physical Review, vol. v., Nos. 27 and 28, Sept. and Oct. 1897. 



