PROCEEDINGS 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 



April 26, 1858. 



Professor Challis made a communication " On the Annular Eclipse 

 of the Sun, March 15, 1858." 



The Master of Trinity read a paper " On Barrow, and his Acade- 

 mical Times." 



May 10, 1858. 



Professor Miller made communications — (1) " On an improved 

 Method of finding the position of any face of a Crystal belonging to 

 the Anorthic System." (2) " On the direction of the Axis of a Zone." 

 (3) On a substitute for the Reflective Goniometer." 



Mr. Godfray read a paper " On a Chart and Diagram for facilita- 

 ting Great-Circle Sailing." 



It has long been known that in many cases a very great saving of 

 distance would be effected by guiding the ship along the arc of a 

 great circle instead of following the rhumb ; but the tedious calcula- 

 tions which great-circle sailing requires, and the difficulty of tracing 

 the track on the chart, have hitherto stood in the way of its adop- 

 tion. The great advantage which Mercator's sailing offers in these 

 respects sufficiently explains the preference given to it, even by those 

 who are fully aware of the longer route it obliges them to follow. 



The object of this communication was to show how the same ad- 

 vantages are secured to great-circle sailing by the adoption of a chart 

 on the central or gnomonic projection, which, with the addition of 

 a diagram, solves the problem of this sailing with the same facility 

 as Mercator's chart does for sailing on a rhumb. 



The great-circle track becomes a straight line joining the two 

 places ; and this being drawn, the various courses and the distances 

 to be run upon each are obtained, as also the distance from the ship 

 to her destination, by a mere inspection of the diagram and without 

 calculation. 



No. XIV. — Proceedings of the Cambridge Phil. Soc. 



