ASTRONOMY AND METEOROLOGY. 869 



hitherto unparalleled. Originating in topographical survey in Esth- 

 onia and Livonia, and commenced in 1816, the operation, both 

 geodesieal and astronomical, have been completed between Izraail on 

 the Danube and Fugleness in Finnmarken, an extent of 25^ merid- 

 ional degrees. Next to this in extent is the Indian arc of 21 21', 

 between "Cape Comorin and Kaliana ; and the third is the French arc 

 of 12 22'. It appears by a note presented to the Imperial Acad- 

 emy of Sciences at St. Petersburg!! by M. Struve, that a pro- 

 visional calculation has been made of a large part of the 

 great aro of Eastern Europe, and that it has been found to indicate 

 for the figure of the earth a greater compression than that derived by 

 Bessel in 183 7 and 1841, from all the arcs then at his command, - 

 Bessel's compression having also been greater than Laplace's previous 

 deduction. 



OBSERVATIONS OX THE ZODIACAL LIGHT. 



MR. I\. II. BIRT submitted to the British Association at their last 

 meeting, a series of observations on the Zodiacal light, made at the 

 Kew Observatory. It appeared to the author that two very impor- 

 tant features presented themselves in connexion with the observations : 

 viz., the position of the great mass of light being constantly north of 

 ecliptic, and the apparent change in the form of the light, or at 

 least that portion of it forming the apex of the luminous triangle 

 on the cone of light, which is very perceptible in the groups of obser- 

 vations, those in February presenting a narrower cone, the axis being 

 very perceptibly inclined to the ecliptic. In this respect these obser- 

 vations are in decided contrast with those of March, when the cone of 

 light had become much larger, the apex more rounded, and the incli- 

 nation of the axis to the ecliptic changed. It would appear from the 

 projections that accompanied the observations, that while the great 

 mass of light was still northward of the ecliptic the direction of the 

 axis was so inclined that it occupied a different position with respect 

 to the ecliptic than it did in February. In the month of April the 

 author considered the axis of the zodiacal light to be slightly north of 

 the ecliptic, the northern side of the cone still exhibiting the greatest 

 luminosity. The contrast of these observations in this month (April) 

 with those in February, is very remarkable ; the cone had become 

 very considerably enlarged, and consequently much broader than the 

 cone seen in February. Two observations, those of March 3 and 

 April 10, were particularized as indicating that under peculiar circum- 

 stances we see more of the zodiacal light than is presented to us 

 ordinarily. In connexion with these phenomena the author observed 

 earlier in March a sudden brightening of the light for an instant, and 

 also variations in its lustre of intermittent character. These inter- 

 missions of brightness were observed on the same evenings at Notting- 

 ham. They are described by the author not to be of the nature of 

 pulsations in the usual acceptation of the term, but to consist of alter- 

 nate brightenings and dimmings of the entire mass of light such as 

 might be produced by the approach and recess of a luminious body. 



