88 



Governor Hennessy's Observations on the 



[Recess. 



given may prove to be of some interest to your Lordship and to the men 

 of science in England. 



Before closing my despatch I received from Capt. Reed the error of the 

 chronometer-watch used for taking the time. It was fast on the mean 

 time at Barram Point h 4 m 8 s - 7. 



I have the honour to be, My Lord, 



Your Lordship's most obedient humble Servant, 

 (Signed) J. Pope Hennessy, 



Governor of Labuan, and Consul-General 

 in the Island of Borneo. 



To the Right Honourable Lord Stanley, M.P., 

 Secretary of State for Foreign Affairs, 



[Note. — The phenomenon of the sun's crescent reflected on to the disk 

 of the moon would seem to have been something accidental, perhaps (if 

 seen by the writer only) a mere ghost, depending on a double reflection 

 between the glasses of his instrument. The figure represents the " reflected" 

 image as in the same position as the crescent itself, not reversed, indicating 

 either a refraction or a double reflection. 



The slender beams of light or shade shooting out from the horns of the 

 crescent would seem to admit of easy explanation, supposing them to have 

 been of the nature of sunbeams, depending upon the illumination of the 

 atmosphere of the earth by the sun's rays. The perfect shadow, or umbra, 

 would be a cone circumscribing both sun and moon, and having its vertex 

 far below the observer's horizon. Within this cone there would be no 

 illumination of the atmosphere, but outside it a portion of the sun's rays 

 would be scattered in their progress through the air, giving rise to a faint 

 illumination. When the total phase drew near, the nearer surface of the 

 shadow would be at no great distance from the observer; the further 

 surface would be remote. Attend in the first instance to some one plane 

 passing through the eye and cutting the shadow transversely, and in this 

 plane draw a straight line through the eye, touching the section of the 

 cone which bounds the shadow ; and then imagine other lines drawn 

 through the eye a little inside and outside this. In the former case the 

 greater part of the line, while it lay within the lower regions of the atmo- 

 sphere, would be in shadow, the only part in sunshine being that reaching 

 from the eye to the nearer surface of the shadow ; but in the latter case the 

 line would be in sunshine all along. In the direction of the former line, 

 therefore, there would be but little illumination arising from scattered 

 light, while in the direction of the latter the illumination would, com- 

 paratively speaking, be considerable. In crossing the tangent there would 

 be a rapid change of illumination. Now pass on to three dimensions. 

 Instead of a tangent line we shall have a tangent plane, and there will 



