The equation, or difference between the true and apparent time, was 1 minute 54 seconds.-The total ingress, being before the Sun rose, could not be seen.

At Tobolsk in Siberia, Mr. Chappe observed the total ingress to be at 7 hours 0 minutes 28 seconds in the morning, and the beginning of egress to be at 49 minutes 20 seconds after 12 at noon.-So that the whole duration of the transit between the internal contacts was 5 hours 48 minutes 52 seconds, as seen at that place; which was 2 minutes 3 seconds less than as seen at Hernosand in Sweden,

At Madras, the Reverend Mr. Hirst observed the total ingress to be at 7 hours 47 minutes 55 seconds apparent time in the morning; and the beginning of egress at 1 hour 39 minutes 38 seconds past noon. The duration between these two internal contacts was 5 hours 51 minutes 43 seconds.

Professor Mathenci at Bologna observed the beginning of egress to be at 9 hours 4 minutes 58 seconds.

At Calcutta (latitude 22° 30' north, nearly 92° east longitude from London) Mr. William Magee observed the total ingress to be at 8 hours 20 minutes 58 seconds in the morning, and the beginning of egress to be at 2 hours 11 minutes 34 seconds in the afternoon. The duration between the two internal contacts 5 hours 50 minutes 36 seconds.

At the Cape of Good Hope (1 hour 13 minutes 35 seconds east from Greenwich) Mr. Mason observed the beginning of egress to be at 9 hours 39 minutes 50 seconds in the morning.

All these times are collected from the observers' accounts, printed in the Philosophical Transactions for the year 1762 and 1763, in which there are several other accounts that I have not transcribed.→→ The instants of Venus's total exit from the Sun are likewise mentioned; but they are here left out, as not of any use for finding the Sun's parallax,

Whoever compares these times of the internal contacts, as given in by different observers, will find such difference among them, even those which were taken upon the same spot, as will shew, that the instant of either contact could not be so accurately perceived by the observers as Dr. HALLEY thought it could; which probably arises from the difference of people's eyes, and the different magnifying powers of those telescopes through which the contacts were seen. If all the observers had made use of equal magnifying powers, there can be no doubt but that the times would have more nearly coincided; since it is plain, that supposing all their eyes to be equally quick and good, they whose telescopes magnified most, would perceive the point of internal contact soonest, and of the total exit latest.

Mr. Short has taken an incredible deal of pains in deducing the quantity of the Sun's parallax, from the best of those observations which were made both in Britain and abroad: and finds it to have been 8".52 on the day of the transit, when the Sun was very nearly at his greatest distance from the Earth; and consequently 8".65 when the Sun is at his mean distance from, the Earth.-And indeed, it would be very well worth every curious person's while to purchase the second part of Volume LII. of the Philosophical Transactions for the year 1763; even if it contained nothing more than Mr. Short's paper on that subject.

The log. sine (or tangent) of 8".65 is 5.6219140, which being subtracted from the radius 10.0000000, leaves remaining the logarithm 4.3780860, whose number is 23882.84; which is the number of semidiameters of the Earth that the Sun is distant from it. And this last number, 23882.84, being multiplied by 3985, the number of English miles contained in the Earth's semidiameter, gives 95,173,127 miles for the Earth's mean distance from the Sun.But because it is impossible, from the nicest obser

vations of the Sun's parallax, to be sure of its true distance from the Earth within 100 miles, we shall at present, for the sake of round numbers, state the Earth's mean distance from the Sun at 95,173,000 English miles.

And then, from the numbers and analogies in § 11 and 14 of this Dissertation, we find the mean distances of all the rest of the planets from the Sun in miles to be as follows: --Mercury's distance, 36, 841, 468; Venus's distance, 68,891,486; Mar's distance, 145,014,148; Jupiter's distance, 494,990,976; and Saturn's distance, 907,956,130.

So that by comparing these distances with those in the tables at the end of the chapter on the solar system*, it will be found that the dimensions of the system are much greater than what was formerly imagined and consequently, that the Sun and the planets (except the Earth) are much larger than as stated in that table.

The semidiameter of the Earth's annual orbit being equal to the Earth's mean distance from the Sun, viz. 95,173,000 miles, the whole diameter is 190,346,000 miles. And since the diameter of a circle is to its circumference as 1 to 3.14159 the circumference of the Earth's orbit is 597,989.090 miles.

And, as the Earth describes this orbit in 365 days 6 hours (or in 8766 hours), it is plain that it travels at the rate of 68,217 miles every hour, and consequently 11,369 miles every minute; so that its velocity in its orbit is at least 142 times as great as the velocity of a cannon-ball, supposing the ball to move through 8 miles in a minute, which it is found to do very nearly;—and at this rate it would take 22 years 228 days for a cannon-ball to go from the Earth to the Sun.

On the 3d of June, in the year 1769, Venus will again pass over the Sun's disc, in such a manner,

* Fronting page 72.

as to afford a much easier and better method of investigating the Sun's parallax than her transit in the year 1761 has done. But no part of Britain will be proper for observing that transit, so as to deduce any thing with respect to the Sun's parallax from it, because it will begin but a little before sun-set, and will be quite over before 2 o'clock next morning.The apparent time of conjunction of the Sun and Venus, according to Dr. HALLEY's tables, will be at 13 minutes past 10 o'clock at night at London; at which time the geocentric latitude of Venus will be full 10 minutes of a degree north from the Sun's centre-and therefore, as seen from the northern parts of the Earth, Venus will be considerably depressed by a parallax of latitude on the Sun's disc; on which account, the visible duration of the transit will be lengthened; and in the southern parts of the Earth she will be elevated by a parallax of latitude on the Sun, which will shorten the visible duration of the transit, with respect to its duration as supposed to be seen from the Earth's centre; to both which affections of duration the parallaxes of longitude will also conspire.-So that every advantage which Dr. HALLEY expected from the late transit will be found in this, without the least difficulty or embarrassment.-It is therefore to be hoped, that neither cost nor labour will be spared in duly observing this transit; especially as there will not be such another opportunity again in less than 105 years afterward.

The most proper places for observing the transit, in the year 1769, is in the northern parts of Lapland and the Solomon Isles in the great South- Sea; at the former of which, the visible duration between the two internal contacts will be at least 22 minutes greater than at the latter, even though the Sun's parallax should not be quite 9"If it be 9" (which is the quantity I had assumed in a delineation of this

transit, which I gave in to the Royal Society before I had heard what Mr. Short had made it from the observations on the late transit), the difference of the visible durations, as seen in Lapland and in the Solomon Isles, will be as expressed in that delineation; and if the Sun's parallax be less than 9" (as I now have very good reason to believe it is), the difference of durations will be less accordingly.