330 PHILOSOPHICAL TRANSACTIONS. [aNNO 1793c 



to be built very lofty. I am sorry to remark that, as far as my observation has 

 gone, this light has never appeared clear and bright, as a light to direct ships 

 ought to do. 



5th. It would be worth perhaps the attention of government to send a vessel 

 with time-keepers on board, in order to examine and note the soundings between 

 the parallels of Scilly and Ushant at least ; from the meridian of the Lizard 

 point, as far west as the moderate depths extend ; I mean such as can be ascer- 

 tained with exactness in the ordinary method of sounding. I have reason to 

 suppose that our chart of soundings is very bad ; and indeed how can it be other- 

 wise, considering the imperfect state of the art of marine surveying at the time 

 when it was made ? A set of time-keepers will effect more in the course of a 

 summer, in the hands of a skilful practitioner, than all the science of Dr. Halley 

 during a long life ; for who could place a single cast of soundings, in the open 

 sea, without the aid of a time-keeper ? The current in question must have dis- 

 turbed every operation of this kind. It should be the task of the person so 

 employed, to note all the varieties of bottom, as well as the depths ; the time of 

 high and low water ; setting of the tides, and currents, &c. Such a survey, 

 skilfully conducted, might enable mariners to supply the want of observations of 

 latitude, and of longitude ; and of course to defy the current, as far as relates 

 to its power of misleading them. 



6th. It is certain that the current in question may be somewhat disturbed by, 

 or rather will appear to be blended with the tides, at the entrances of the British 

 and St. George's Channels ; but it is obvious that the current will have the same 

 effect in setting a ship out of her course, as if no tide existed ; because, what- 

 ever effect one tide may have, the next will nearly do away. But there are two 

 particulars, well worth ascertaining ; and these are, first the point at which the 

 2 tides of St. George's and of the British Channel separate, on the west of Scilly. 

 And '2dly, what degree of northing one of the streams has, more than the other. 

 Because a ship, in approaching Scilly from the west, on a flood tide, and keep- 

 ing in a parallel which may be to the north of the point of separation of the 2 

 tides, and consequently in the tide stream of St. George's Channel may be thrown 

 too far to the north ; though had she been far enough to the west to receive the 

 effect of the next ebb, this temporary and alternate derangement of the course 

 would have had no ill effect ; or even have been noticed. But admitting that a tide, 

 with any degree of northing in it, does take place to the west of Scilly ; this will 

 furnish an additional reason for keeping in a southern parallel. 



XFIII. Observations on the Planet Venus. By William Herschel, LL.D., 



F.R.S. p. 201. 

 The planet Venus, says Dr. H., is an object that has long engaged my par- 



