It is finally determined that we shall enter upon the Business of adjusting the Boundary Line between Penna. and Virginia in June. We had given Orders for the Importation of valuable Instruments for this Purpose, and also for the Connoissance des Temps and nautical Almanach. But we have been disappointed by the extreme Severity of the Winter. They cannot arrive in Time. The Pennsylvanians rather than protract the Business, have agreed to furnish Instruments for the Eastern End. I shall go the western, with what we have here. But as the Books mentioned will be necessary, I resolved to request your Assistance in procuring both, or one of them, if they could possibly be had. I thought you might probably be able to effect this, from your Connections at Philada. Annapolis or New York. The Conn: des Temps is frequently to be met with on Board the French Ships, always on those belonging to the King. I have here requested a Merchant to endeavour to procure a copy, but doubting of Success, must beg your favourable Assistance also. The Loss of my De la Lande from whose Tables, Calculations might easily have been made, renders one or other absolutely necessary, unless indeed the Pennsylvanians may have procured them. Besides the Eclipses of Jupiter’s Sat. they will be necessary in many other Respects.

Your Letter to Dr. McC. has put us also upon attempting an aerial Voyage; we have not yet however been able to ascend. I find the Air from Straw much more inflammable than any I ever collected from Wood &c., but have not been able to observe that extreme Levity, which must be necessary for the Purposes of a Balloon. A Gun Barrel is what I have hitherto used, for we do not understand the Method used in France for collecting such vast Quantities of it. If you should have been informed relative to this, should be most obliged for your Communication.

I am sorry that I have not been able to continue my Therm. Observations. The Thermometer was borrowed and sent for about a month past. The Diary ends 30th. March—began 16th. Jany. It is impossible to procure one here, but I expect that which I ordered from England about June.

The Comet I mentioned in my last cross’d the Eclipse about 23° ½ in Pisces. It’s Course was a little inclined to the East of North. It’s Motion was about 1°15′15″ in 24 Hours. The last Observation I made upon it was the 12th. of Feby. when I measured its Distance from γ in Pegasus. But the Weather was so cold as to render the Use of Instruments almost impracticable. The Light of the Moon also greatly obstructed Observation at the most critical Time.

I am Dr. Sir, with the greatest Respect & Esteem, Yr. Friend & Servt.,