50 PHILOSOPHICAL TRANSACTIONS. [aNNO]78I. 



to 5 miles wide, and but for its freshness might pass for an arm of the sea. 

 Common description fails in an attempt to convey an adequate idea of the gran- 

 deur of this magnificent object. 



I have already endeavoured to account for the singular breadth of the Megna, 

 by supposing that the Ganges once joined it where the Issamutty now does; and 

 that their joint waters scooped out its present bed. The present junction of these 

 two mighty rivers below Luckipour, produces a body of running fresh water, 

 hardly to be equalled in the old hemisphere, and, perhaps, not exceeded in the 

 new. It now forms a gulf interspersed with islands, some of which rival, in 

 size and fertility, our Isle of Wight. The water at ordinary times is hardly 

 brackish at the extremities of these islands ; and, in the rainy season, the sea, 

 or at least the surface of it, is perfectly fresh to the distance of many leagues 

 out. 



The Bore (which is known to be a sudden and abrupt influx of the tide into 

 a river or narrow strait) prevails in the principal branches of the Ganges, and in 

 the Megna ; but the Hoogly River, and the passages between the islands and 

 sands situated in the gulf, formed by the confluence of the Ganges and Megna, 

 are more subject to it than the other rivers. This may be owing partly to their 

 having greater embouchures in proportion to their channels, than the others 

 have, by which means a larger proportion of tide is forced through a passage 

 comparatively smaller ; and partly to there being no capital openings near them, 

 to draw off any considerable portion of the accumulating tide. In the Hoogly 

 or Calcutta River, the Bore commences at Hoogly Point, the place where the 

 river first contracts itself, and is perceptible above Hoogly Town ; and so quick 

 is its motion, that it hardly employs 4 hours in travelling from one to the other, 

 though the distance is near 70 miles. At Calcutta it sometimes occasions an 

 instantaneous rise of 5 feet : and both here, and in every other part of its track, 

 the boats, on its approach, immediately quit the shore, and make for safety to 

 the middle of the river. 



In the channels, between the islands in the mouth of the Megna, &c. the 

 height of the Bore is said to exceed 12 feet ; and is so terrific in its appearance, 

 and dangerous in its consequences, that no boat will venture to pass at spring 

 tide. After the tide is fairly past the islands, no vestige of a Bore is seen, which 

 may be owing to the great width of the Megna, in comparison with the passages 

 between the islands ; but its effects are visible enough by the sudden rising of the 

 tides. 



X. Astronomical Observations on the Rotation of the Planets round their Axes, 

 made ivith a View to determine whether the Earth's Diurnal Motion is perfectly 

 Equable. By Mr. William Her schel, of Bath. p. 115. 

 The various motions of the planet we inhabit; the annual revolution in its 



