A difficulty is, however, denoted.  “My duties here,” he writes, “as they engross everything at present, will force me to delay a little, and I am in hopes, by so doing, to obtain some further data.  I enter, in a few days, on the discharge of my professional duties, under considerable disadvantages, owing to the late introduction into our courses of some French works on the highest branches of mathematics, which it falls to my lot first to teach.  Between French, therefore, and fluxions, and moreover, the French method of fluxions, which is somewhat peculiar, I have had my hands pretty full.  I look forward to a respite in April.”

The professor had, in fact, to teach his class as he taught himself, and just kept ahead of them—­a very hard task.

In the mean time, while this plan of an enlarged publication was kept in view, I pushed my narrative forward.  While it was going through the press, almost every mail brought me something of interest respecting the progress of scientific discovery.  A few items may be noticed.

Discovery of Strontian on Lake Erie.—­Mr. William A. Bird, of Troy, of the Boundary Survey, writes (Jan. 22d):—­

“On our return down the lake, last fall, we were becalmed near the islands in Lake Erie.  I took a boat, and, accompanied by Major Delafield, Mr. A. Stevenson, and Mr. De Russey (who was to be our guide), went in search of the strontian to the main shore, where Mr. De Russey says it was found in the summer of 1819.  After an unsuccessful search of an hour, we gave it up, and determined to return to our vessel.  On our way we stopped at Moss Island, when, immediately on landing, we found the mineral in question.  I wandered a little from the others, and found the large bed of which I spoke to you.  We there procured large quantities, and some large crystals.

“This strontian was on the south side of Moss Island, in a horizontal vein of three feet in thickness, and from forty to fifty feet in length.  I had no means of judging its depth into the rock.  The base of the island is wholly composed of limestone, in which shells scarcely, if ever, appear.”

Conchology—­Mineralized Fungus, &c.—­Dr. Samuel L. Mitchell, of New York, writes (Jan. 30th):  “I was glad to receive your letter and the accompanying articles, by the hand of Colonel Gardiner; but I am sorry your business is such as to prevent your meditated visit to the city until spring.

“I had a solemn conference with Mr. Barnes, our distinguished conchologist, on the subject of your shells.  We had Say’s publication on the land and fresh water molluscas before us.  We believed the univalves had been chiefly described by him; one, or probably two of the species were not contained in his memoir.  It would gratify me very much to possess a complete collection of those molluscas.  I gave Mr. Barnes, who is an indefatigable collector, such duplicates as I could spare.