As to the Journals, I should not much object to engage that a sheet or more should be ready for publication every week; but I conceive that it would give them additional importance if it were left to the direction of the professor, with the approbation of the committee, with proper notice, to publish a number at the end of a fortnight, instead of a week, whenever there might appear to be a real deficiency of matter to fill it. And I think I should want little or no assistance, either in translating or in transcribing, except what Mr. Davy might have the goodness to give me. I hope that, when you have reconsidered what I have stated, you will not much differ from me in opinion, and that you will favour me with a further communication of your sentiments on the subject. I am, Sir, your obliged and obedient humble Servant, THOMAS YOUNG. Count Rumford, Royal Institution. DR. THOMAS YOUNG TO SIR JOSEPH BANKS. Worthing, September 10, 1810. DEAR SIR,--Observing from the papers that you have been interesting yourself respecting the arrangement of a micrometer for the purpose of measuring the diameter of the fibres of different kinds of wool, I beg leave to trouble you with the description of a very simple instrument which I invented some time ago for a similar purpose, and which I propose to call an agricultural micrometer. I should imagine it to be sufficiently accurate for all practical purposes, and the great facility and cheapness of its construction may perhaps render it useful to a class of persons who would object to the expense of providing themselves with a more complicated apparatus. If it appear to you in the same point of view, you will be pleased to make any use that you may think proper of this communication. When we look at a distant candle through a lock of wool it appears surrounded by rings of colours, and these rings are invariably so much the larger as the wool is the finer. The cause of these appearances I have endeavoured to explain in my lectures and elsewhere; but for the present purpose the principal object is to ascertain their comparative magnitude. In order to perform this I take a card blackened on one side, describe on it two concentric circles, the outer exactly one inch in diameter, the inner 11/20, make at the centre a hole about 1/20 of an inch in diameter, and pierce the card at the circumference of the inner circle, in 10 or 12 points at equal distances, with a small pin, and at that of the larger in 7 or 8 points, at unequal distances, with a large one. I then take a small rod of wood about a yard long and divide it into half-inches, numbering them from one end, at which I fix two or three pins side by side and wind round it a piece of wire--for instance a common knitting needle--in such a form as to hold the card upright between its ends and to slide on the rod. This is the whole apparatus.