550 OBSERVATIONS ON TllE ZODIACAL LIGHT 



No. 275 

 JANUARY 8tli, 1855: EVENING. 



Lat. 6 47'N. : L.m. 79 31' W. 

 Sun set at b/i. 'rim. 



Stronger Ligbt at/"' m - &c '" to } Diffuse at 71,. 15w., &c. 

 SUB'S Ion. 287 42'. 



Yesterday was Sunday. Clouds in west, this evening, till after 7 h , when the sky cleared off, and became extremely 

 favorable for observations. It will be seen by reference to the chart, that the ecliptic is, at that hour, nearly perpen- 

 dicular to the horizon. At 7' 15" the effulgent Light bslow the zigzag was remarkably bright. I took the boundaries 

 as in the chart, but in fifteen minutes after was surprised to find that already they were considerably extended; and 

 I began to query whether there were not pulsations. At 7" 3(J in I was satisfied that there were ; for the Light was 

 now back at the first boundary a a, and had dimmed considerably. My record from this was as follows: 



h. m. /* m. 



"At 7 39, brightening. 



7 42, at b, and bright ; has brightened most deci- 



ledly since 7" 39 ra . 



< 



7 50, decide-illy dimmed, compared with 7' 1 42 m . 

 7 52, has brightened and dimmed again in the last 

 2 minutes. 



At 7 54, has brightened and dimmed once more since 



last. 

 7 55|, bright, and at b. 



7 58|, still bright. 



8 o'clock, still so. 



At 8" 8 ra still bright, and its boundaries at c. A change has come over it in the last eight or ten minutes. It has 

 extended its boundaries to c c, and the upper part has become decidedly brighter than at any time before. In the 

 early part of the evening, say at 7" 15 m , the portion below the zigzag was extremely bright; while the upper was 

 dimmed off, till it was very difficult to make out its highest portions. Now, the lower part is not strikingly bright; 

 while the upper portions, as just remarked, have increas'.-d in brightness, so that it is easy to trace them. This has 

 been since the pulsations ceased." I neglected to notice when the great effulgence below ceased. At 8 h 30 m boundaries 

 still well marked. At 10 h 30 m , perhaps a paleness in that part of the sky, but nothing decisive. In noticing these 

 pulsations, I was assisted by one of the petty officers of the ship : he had no difficulty in observing the changes of 

 the brightness. 



