About a week ago the papers whereof that herewith Mark’t A is a Translation were sent to Peruse, and on my returning them With a Translation I beged Leave to Communicate Coppies of them to You and Dr. Colden with Liberty if you thought proper to print them or any Part of them. In Answer To which I obtained the Leave coppied at the end of Them and Struck out La Gallissonieres name, for the reason in the Leave.

The Delay of that Leave put me upon Dipping into the Abridgment of the Philosophical Transactions to see what [was] there said of the matters in those papers, and from thence I made the Extracts in the paper Herewith Mark’t B. by which I find that that which had baffled all the Art of man hitherto To discover with any Tolerable Certainty (Vizt. the Suns Distance from the Earth) may with great Certainty be Discovered by the Transit of Venus over the sun the 26 of May 1761 Old Stile, if well Observed in the East Indies and here and these Observations Compared Together.

It Would be a great honour To our young Colledges in America if they forthwith prepared themselves with a proper apparatus for that Observation and made it. Which I Doubt not they would Severally Do if they were Severally put in mind of it and of the great Importance that that Observation would be To Astronomy and that the missing that One Observation cannot be retrieved for 250 years To come.

You have on so many Occasions Demonstrated Your Love To Literature and the good of Mankind in General that I thought no person so proper as your self to think of the ways and means of perswadeing these Colledges to prepare themselves for taking that Observation and in order to it you may make what use you please of the papers herewith, only not my name. Endorsed: Coppy Letter to Mr Franklin Janry 29 1753

What Put me upon giveing you the Trouble of this Was the Sight which a few Days agoe I had of some Letters from the Royall Academy of Sciences at Paris with directions for Observing in Canada the End of a Transit of Mercury over the sun Which is To happen on the 6. of may Next and by their Estimation about ¾ past five in the morning at Quebeck and that it Ends at or possibly before sun riseing at the Lac Superieur.

This made me Look into Lowthorpes Abridgment of the Transactions of the Royall Society at London page 431. and by that in the Longitude of 5° West of London, (Which I suppose is nearly the Longitude of Phileadelphia as New York by many Observations of the Eclipses of Jupiters first Satellite Was found in 4h. 56’ nearly) it would seem To me that the Transit would End three minutes after Five in the morning, but if it does, yet both Interior and Exterior Contacts at the end, may be seen at Phileadelphia and here the transition may be Seen some minutes before the Contacts, or yet Still Longer in Connecticut, Boston, Halifax, and Louisbourgh by reason of their Greater Latitudes and Less Longitudes.

The Jesuits in China and the East Indies I doubt not will Observe it in Sundry places there as the Whole Continuance of Mercury on the sun will be there Visible and if well Observed there and the End well Observed in North America it will bid the fairest of anything hitherto had To give the Suns parrallax or distance from the Earth, for the Triangles made of the Observations in the East Indies With those here will have known Bases of above ¾ of the Diameter of the Earth; the Next Transit by page 432 is in 1756 but It will not be visible here.

But the Critical Time for Obtaining the suns Parrallax will Be the Transit of Venus over the sun (by page 436) the 26 of May 1761 Old Stile which in 5h. west Longitude I Esteem will end at 53’ after 4 in the Morning and be visible at Phileadelphia for ¼ of an hour after Sun rise and much Longer Northward and Eastward.

Jones’s Abridgment of the Transactions, Vol. 4 page 213 &ca. has a Discourse of Edmund Halley concerning that transit of Venus and a figure of it and by good Observations of that, he Says, the parrallax of the sun may be Ascertained to whereas I doubt of it’s Being Certain now To ¼ for Halley there Supposes it May be 12½ Seconds Wheras Flamstead in Sundry places of the Transactions from his Observations of Mars when nearest the Earth Esteems it not To Exceed 10'’.

By Transactions Vol: I, 435 and 436 you’ll see that No Transit of Venus till the year 2004 Will be visible both here and in the East Indies at the Same time so that if this Opportunity be missed there Will be None so good for 250 Years To Come To Ascertain this Much Desired points of the Suns parrallax which being Known The parrallax of all the planets is of Course from thence found.

As there are Now Sundry Nurseries of Learning Springing Up in Pensilvania, Jersey, New York, Connecticut, and Boston; all ways Should be thought of To Induce each of those To provide a proper apperatus for makeing such Observations, Long before the year 1761 that they May be Expert at Takeing Observations of the Kind before that Transit Happens; and in the mean time To be Ascertaining the Longitudes of these places by Observations of the Eclipses of Jupiters first Satellite and the Latitudes of the places by good Quadrants for these things should Be Known and Ascertained to Render the Observations of the Transit of use for Ascertaining The parrallax.

Another Reason why preparation should be made in all these places for that Rare Event, is; that should it happen to be Cloudy in some of these places yet it may be Clear in Others and by means of them that have Clear weather the Great End may be Gained; that Event may Well be Called Rare as Horrox who says the Last Transit of Venus over the sun On November 24 1639 now 114 years ago is the Only one of the Posterity of Adam who has seen one of these Transits.

I have said before that the suns Parrallax is not Ascertained To ¼ part but it seems there is a much greater Difference in Opinion about it than that, for tho’ it be Generally Taken now to be 10’ yet the Book called Matho or the Cosmotheoria puerilis printed in 1740 Vol: 2 page 388 &ca. gives very plausible Reasons why it Cannot be Less than 20'’ and he thinks 26'’ a more Reasonable Number. For he shows that if the parrallax be Only 10'’ then the point of Equall Attraction Between the Sun and Earth, is but 45 Semidiameters of the Earth Distant from the Earth but the moons Distance is about 60 and therefore 15 SemiDiameters in it’s Conjunction Nearer the Sun than the point of Equall Attraction and from thence he Concludes that as there the Attraction is greater To the sun than to the Earth it Could Never Adhere To the Earth but be Drawn from it Towards the sun and allowing the parrallax to be 20'’ yet even in that Case the moon Would be sometimes Beyond the point of Equal attraction and 26'’ Should be allowed To Keep it always within that Point, which Reasons prevailed with me to be of his Opinion Till I Saw Mr. Maclaurins Explanation of Sir Isaac Newtons philosophy which Demonstrates Clearly that tho’ the moon Goes Without the point of Equall Attraction as Matho says, Yet it Will Adhere To the Earth by Means of its projectile free in its Orbit Round the Sun.

To Point out what apparatus of Instruments should be procured I Know of Nothing Better than To referr to the Abridgments of the Philosophical Transactions where multitudes of Observations of the Heavenly Bodys appear and the Instruments they were Observed with and how, And as To the Observations of the Transit of Mercury in particular and Instruments the Observers made use of, You’ll see Largely in the Abridgment of Philosophick Transactions Vol: 8 page 194 To 208 and Vol: 4. 213 &ca. before mentioned.

Each of these places which have not a Set of the Abridgments of the Philosophick Transactions should in the first place Get them Being in 9 Vol: quarto which as they will be Cheaper so will they be Much Easier To Turn To, than the Transactions themselves by Means of their Tables.

I find by the preface To Halleys Tables page 3 that No. 386 of the Transactions Contains Halleys Corrections of his Numbers of Mercury. But that Volume 6 Containing that Number I have Lent To a Gentleman Living at 70 miles Distance from here.

I Find by Halleys Tables that Macao in China is in 7h. 35’ and Pekin in China in 7h. 45’ East Longitude yet by reason of their Northern Latitudes and the suns Northern Declination at the times of Both the preceeding Transits they may see the ends of them Before the Sun Setts in those places.

I have Computed what would be the Lengths of the Bases of triangles made of Observations at Phileadelphia and Observations in the following places in the East Indies, and found them as follows

On the papers of Directions herewith Mark’t A I Would Observe that I think them very good and that I find all or most of them in the Transactions and that if the Observer is acquainted With makeing Observations of that Kind they Seem Rather Too particular. If he is not acquainted, then the Neglect of Mentioning the Smoaking the Eyeglass before he Looks at the Sun thro’ the Telescope and Quadrant (if they have not Smoak’t plain Glasses fitted without the Eyeglass) may run the Observer into the Danger of Looseing an Eye. If he is to Observe the figure of the Sun Cast on a paper thro’ the Telescope then the Darkning of the Room should have Been mentioned.