engage men for the management of their engines, and see that they are properly instructed in the use of them; and one man as foreman over the rest; who, though they might follow their usual occupations, should be always ready, upon every alarm of fire. The engines, and every part of the apparatus, should be examined, and the engines played, every three months at least, to keep them in order, and to see that the hose are in good repair. In Paris, the firemen carry strong twine in their pockets, with which they bind the hose, should they happen to burst while the engine is at work, which is found a sufficient security. I have known engines taken several miles into the country, and when arrived at the fire, so much out of order as to be entirely useless!

The builder of every house should consider that it may, one day, be burnt down; it should therefore, if large, have two staircases, as many partywalls as can be conveniently admitted, and the partitions should be brick-nogged, the walls should be stuccoed, and not wainscotted; and the communication from one part to another, as simple and direct as possible; every house should have a parapet, and an easy mode of ascent to it.

Composition floors are of essential service in resisting the progress of fire; they should therefore be introduced wherever it may be practicable; thin plates of iron have been recommended beneath the floors, staircases, &c. ; indeed, from the perfection to which our iron, manufacture is car

LETTER CLXXXIV.

From the same.

Edinburgh, June 5, 1789.

Much esteemed Friend,

I regard it as a considerable addition to the honour I have received by the Diploma sent me by the London Medical Society, that it comes accompanied with a very polite and friendly letter from your hand. I should have acknowledged this sooner, but much College business at this time, and other occupations, have prevented me.

I have always considered it as my honour that I once had you for a Pupil, and I am now highly gratified in finding you still retain me in your memory. I take this opportunity of assuring you, that a friendly intercourse shall not fail on my part.

I must now beg that, when you have an opportunity, you will present my most respectful compliments to the Medical Society, and assure them, that I have the highest sense of the honour they have done me; that I am happy to find them going on with their valuable communications to the public, and that I shall not cease my endeavours to promote as far as I can, the valuable purposes of their Institution; and my zeal will certainly be strengthened by your friendly exhorta

tion. But I am sorry to tell you that my time of life, and the occupations and practice of teaching, which I am still engaged in, do not allow me to promise much; and I have engaged I believe too rashly, to promise a communication to the public. I have already begun to prepare a fifth volume of "First Lines," on subjects not touched before. At present I must conclude, with assuring you of the esteem and respect of

Your faithful friend and humble servant,
WILLIAM CUllen.

LETTER CLXXXV.

Dr. GARNETT to Dr. LETTSOM.

Dear Doctor,

London, May 26, 1795.

I have perused with much pleasure and satisfaction the paper which you yesterday put into my hands. It would appear that starch could be made from potatoes much cheaper than from wheat, at the same time that a considerable quantity of wheat would be saved to the public. In the first page, line 4th from the bottom, I have taken the liberty with a pencil to insert the word "wheat;" for it is evident that Dr. S. wishes to compare the product of an acre of potatoes with that of an acre of wheat: the word has been omitted through mistake, for without it the sentence is perfectly ob

scure. If you could ascertain the quantity of starch extracted from a given weight of wheat, then might the advantage of making starch from potatoes be accurately calculated. From the estimate given, which I doubt not is as accurate as it can be made, the difference in the expence between an acre of potatoes and the same quantity of wheat is only 18s. while the quantity of potatoes produced is 300 bushels, and of wheat 30.

The fecula would probably produce the greatest advantage by being fermented and distilled; but before this subject can be decided upon, experiments ought to be made on a large scale. Could you not cultivate an acre or two of your ground with potatoes? this would enable you to ascertain various circumstances relative to agriculture, and political economy, of the greatest importance to mankind.

The theory of fermentation, which has puzzled philosophers ever since the phenomenon was observed, is now rationally and easily explained, on the principles of the pneumatic chemistry; and I own I was somewhat surprised to see a man of Dr. Sutcliff's age so thoroughly acquainted with the principles of the new doctrine, as to improve the explanation given by M. Lavoisier, and place it in a much more striking point of view. In the last page, line 12, I should suspect he must mean 4 instead of 3. He wishes to show that neither fecula nor yeast can of themselves easily decompose water, yet jointly they can do

it. For he supposes that the two component parts of the water, the hydrogen and the oxygen, may adhere together, or attract each other with a force of 9, while the attraction of the feculum for the oxygen of the water is only 5; no decomposition will therefore take place. If yeast be added to water, no decomposition likewise takes place, because yeast attracts the oxygen of water only with the force of 4; but if both yeast and fecula act together, their attraction for the oxygen of the water will together be 9; which is rather greater than the force by which the component parts of the water are held together; and this will occasion a slow decomposition, which will leave the hydrogen of the water enveloped in a little undecomposed water and mucilage of the fecula; or, in other words, in the form of a viscous liquor. But if we suppose that the attraction of the yeast for the oxygen of the water is only 3, then the joint action of the fecula and yeast will only be 81, which will be insufficient to separate the component parts of the water which attract each other with the force of 9.

I hope you will excuse the slovenly manner in which these observations have been drawn up; they were, as you may suppose, written in a great haste; and believe me to be, while I have life, Your sincere friend,

T. GARNETT.