296 British Association for the Advancement of Science. 



law of visible direction in monocular vision, it explains all those 

 phenomena of vision by which philosophers had been so long per- 

 plexed ; and that vision in three dimensions received the most 

 complete explanation from Prof W.'s researches. Sir J. Herschel 

 characterized Prof. W.'s discovery as one of the most curious and 

 beautiful for its simplicity, in the entire range of experimental 

 optics. 



Rev. Charles Graves read a paper on a General Geometric 

 Method. 



Sir T. M. Brisbane reported the result of an experiment to de- 

 termine the difference of longitude between London and Edin- 

 burgh. Having observed the surprising accuracy with which 

 the difference of longitude of London and Paris had been ob- 

 tained by Mr. Dent's chronometers, he applied to him, and he 

 very liberally placed at his disposal twelve of his valuable chro- 

 nometers. With these, the differences of longitude of London, 

 Edinburgh and Makerstoun, were taken ; and by a mean of all 

 the observations taken in going to the latter station and in return- 

 ing, they were found to differ only by five one-hundredths of a 

 second. 



A letter from the Astronomer Royal, G. B. Airy, was read, on 

 the means of correcting the local magnetic action of the Compass 

 in iron Steam-Ships. By an apparatus of his invention, the 

 local deviations' were almost wholly corrected. The description 

 will probably be given hereafter. 



Prof. Lloyd read a paper entitled, '■' Recalculation of the obser- 

 vations of the Magnetic Dip and Intensity in Ireland^ with ad- 

 ditional elements.'''' It is found that the annual decrease of the 

 dip at Dublin is 2'. 38. The recent and more complete observa- 

 tions of Sabine at London, make the annual decrease there 2'. 40. 

 Major Sabine spoke in reference to the Report on the Yariations 

 in the Magnetic Intensity., printed in the last volume. He ad- 

 verted to the observations of Profs. Bache and Courtenay, made 

 in New York and the adjoining States, and which Prof B. is now 

 engaged in connecting with Europe. Until this comparison is 

 complete, these observations determine the value of the magnetic 

 force at the stations at which they are made, relatively to each 

 other, but not relatively to other parts of the globe. It was for 

 this reason that they were not available for Sabine's Report, 

 which had for its object the general distribution of the magnetic 



