is one of importance in various branches of practical science, the author examines the several theorems which have been proposed for its elucidation, and compares them with the results obtained by experimental researches.

Dr. Papin, in 1686, appears to have first ascertained the law of efflux to be the same for both elastic and inelastic fluids, and the majority of the writers on the subject since his time have adopted as the fundamental data of their calculations, the hydrodynamic law of spouting fluids, by which the velocity of discharge is found to be proportional to the square root of the height of the superincumbent column of homogeneous fluid.

The author investigates particularly the methods of calculation proposed by Dr. Gregory, Mr. Davies Gilbert, Mr. Sylvester, Mr. Tredgold, and M. Montgolfier, and points out the differences which exist in their several methods. That of Mr. Sylvester is the only one which differs in any considerable degree from the simple law above stated; and his calculation is based upon the supposition that the respective columns of light and heavy air represent two unequal weights suspended by a cord, hanging over a pulley by which mode of calculation, in the cases selected by the author for comparison, a result is obtained of only about one-third the amount given by the other methods. These calculations are compared with some experiments made by Sir John Guest at the Dowlais Iron Works, and also of Mr. Dufrenoy at the Clyde and at the Butterly Iron Works, recorded by him in his report to the Director-General of Mines in France. The results are tabulated; giving the pressure of the blast, the area of discharge, the velocity of the blast, the quantity of air ascertained by experiment, and the quantity shown by the several methods of calculation. From all these comparisons the author draws the conclusion that the method of calculation proposed by Montgolfier is the most accurate, as it is also the most simple. If the pressure be ascertained in inches of mercury, it is only necessary to find the column of air in feet equivalent to the pressure, and to multiply this number (as in the common case of gravitating bodies) by sixty-four feet, and then the square root

of this product will give the velocity of discharge in feet per second. The equivalent height of the column of air in feet is found by multiplying the number of inches of mercury by 11,230 and dividing the product by 12, mercury being 11,230 times the weight of air. Allowing for a small loss by friction in the quantity found by experiment, the agreement between the theoretical and experimental quantities is extremely near. Rules are likewise given for applying these calculations to other gasses of different specific gravities, which are also applicable to chimney draughts and to the expansion of air by heat.

Daguerreotype.

The theory of this extraordinary (and in times past would have been considered magical) production, not having been developed by its inventors or discoverers, we gladly avail ourselves of the very ingenious suggestions proposed upon the subject by Martyn Roberts, Esq.; and communicated to the scientific world through the medium of the Philosophical Magazine, No. 117, for April.

The mode of conducting the Daguerreotype process, and its astonishing results in producing permanent pictures on silvered plates, by the reflection of variable intensities of light and shades, having been fully described in our Journal, we proceed, without further preface, to lay before our readers Mr. Roberts's views as to its theory.

"Although the Daguerreotype process has long excited intense iuterest in the scientific world, we have not as yet had an explanation of the wonderful effect produced. I believe that even M. Arago has failed to elucidate the theory; and not only has this great philosopher been foiled, but the inventor of the process is unable to solve the problem; with these facts before me, I feel it almost presumptuous in so humble a votary of science as my

self, to attempt an explanation of the cause of the production of Daguerreotype pictures, but if my attempt has the effect of directing attention to the right path for arriving at a solution of the question, I shall be satisfied. We all know that light has a powerful influence on crystallization; solutions that will not crystallize in the dark, instantly form on the admission of light; the crop of crystals is always more copious on the enlightened side of a glass, containing a crystallized liquid, than on the dark side.* Ice forms more rapidly during moonlight, and on the break of day, than on a dark night; but I need not adduce examples of the influence of light on crystallization, for the fact is allowed by all scientific men.

Let us then suppose, that in the Daguerreotype process, the cleansed silver plate is exposed in the dark to the vapour of iodine; this deposits itself in a flocculent or powdery state on the plate, unable to form the peculiarly shaped iodic crystals, from the absence of light; but yet all other requisites being present, it may be considered in an incipient state of crystallization, or balanced so finely, that the admission of the excitant light instantly throws it into plate-formed iodic crystals, but only in those parts where the light has impinged, and here its perfection of, or continuity of crystallization, is merely in proportion to the intensity of light.

Having now the iodated plate removed from the camera obscura, where it has undergone a surface crystallization, more or less perfect in those parts where the lights and shades have fallen, we submit it to the mercurial vapour; the atoms, vesicles, or globules of this vapour being very minute, attach themselves to all the minute inequalities of face in the iodine; on those parts which are fully crystallized, the vapour is precipitated on the flat tabular surface of the crystals, and here offering a continuous and equal angle of reflection to the eye, it appears white and resplend

* For instance, see the glass show bottles in chemists' windows, containing camphor evaporated, and deposited on the side of the bottle next the window, and not on the reverse side, or that toward the interior of the shop.---ED.

ent. On the non-crystallized or imperfectly crystallized surface of the iodine, which being in a measure powdery and offering no determinate angle of reflection to the eye, the mercurial vapour adheres, but in no flat surface or continuous determinate angle capable of reflecting a mass of light; it may be said it is here unpolished.

Again, may not the angle under which it is necessary to view a Daguerreotype picture, be that of the facet of the iodic crystal, and this be a further confirmation of my theory? The mercurial vapour covers the whole of the iodine, and thus protects it from the further action of light.

Such are the crude views I have formed on this subject, and I trust they may lead to a further elucidation."

Scientific Adjudication.

WOODCROFT'S PETITION FOR THE EXTENSION OF A PATENT RIght. (Continued from page 135, Vol. XVIII.)

Was there no balance sheet in which the accounts were displayed, item by item, so that you could come to a correct balance ?-The balance would depend so much on the value of the machinery.

Of course you would put a value upon the machinery before you drew out that balance sheet, but was there no balance sheet with a debtor and creditor account, to be the foundation and material from which you made out your amount?—Yes, there were accounts submitted by both parties.

I should like to see the balance sheet on which the award was made up; you do not give their lordships exact information whether you put down any value for this patent or not.-It was valued along with the machinery.

Would that paper tell us the value of the machinery, if we had it,-is

there no such paper in existence?—I think not.

Had you the assistance of an accountant?—No, we had not.

Can you take upon yourself to say that you put any value at all upon this patent?—Yes.

What was it then ?-As I stated before, we might estimate this patent at a few hundred pounds; but there was no precise value put upon the patentit was taken in along with the machinery.

Can you tell us what you estimated the machinery at ?-The machinery was valued, as far as regards Mr. Bennett Woodcroft, at £4,000. We considered that to be probably double its value if it had been sold.

You valued it between the two, at double its value?—If sold.

Did you value the patent on the same principle ?-That was to include the patent. So much of the price as was to include the patent, was that valued upon the same principle of double what it might sell for ?-No: I think not. I understood you to say that Mr. Bennett Woodcroft, at this time, had only one third-part of the proprietorship of the patent in him. Is that so? -Yes.

Then that does not agree with the petition. I will read you a part of the petition and then ask you.

The petition states "that on the 7th September, 1831, the partnership was dissolved as to the said John Gould only." Was Mr. Gould formerly in partnership with John and Bennett Woodcroft ?-He was.

Then it recites" that the partnership was dissolved at the date mentioned as to the said John Gould, who thereupon in consideration of the sum of twelve thousand one hundred pounds, paid and secured to him by his former partners, your petitioner and the said Bennett Woodcroft, as and for the value his share and interest in the property and effects of the said partnership, business delinguished and assigned to your petitioner and the said Bennett Woodcroft, all his share in the patent right, machinery, improvements, fixtures, stock in trade, and other effects of the said partnership concern; and after such dissolution the said business of cotton manufacturing, in Manchester, was carried on by the said John Gould and your petitioner, and Bennett Woodcroft took and continued the business of yarn printing in Salford." Was not Mr.John Woodcroft an equal partner with his father in the patent? -No.

How did that appear to you?-If I might be allowed to state the circumstances, that their lordships might really understand the case, I think I could shew in what way it arises. I have been acquainted with these gentlemen five and twenty years. I had been in business at that time, and in business with the house; they often asked me to decide any difference that might arise between them. When Bennett Woodcroft invented this machine he was a servant of Woodcroft and Gould. They furnished the funds for obtaining the patent, and other expenses, and it was considered desirable that the patent should be the property of the concern. I negociated with them on the part of Bennett Woodcroft, the patentee, to allow him to be introduced into the concern as a partner, and to have a small share in the whole of their business, instead of his giving them a license to make goods under his patent. They agreed that he should become a partner, and it was also agreed that the patent, from that time, should become the property of the concern, not the individual property of Mr. Bennett Woodcroft.

That would be put down in writing, of course?—It was.

Mr. Hill: then that must be produced. We cannot hear that at all. Lord Brougham: The learned counsel has got more than he likes. (To the witness): You say two or three hundred pounds might be the value of the patent in the year 1835-do you mean two or three hundred pounds, or from six to nine hundred pounds. Did you mean to speak of Bennett Woodcroft's share, in estimating the value of the patent in 1835, at from six to nine hundred pounds. Do you think it was worth so much at that time?— We made no distinction between the patent and the machinery, for it certainly was not considered of much value at that time, in consequence of the state of the trade.

Do you think, casting your mind back to the year 1835, the patent was worth as much as eight or nine hundred pounds in the year 1835, or only two or three hundred pounds?—I should think that £900 was the full value; £300 for Bennett's share.

You think it was worth as much in 1835 ?-I should think not. Was it worth more than two or three hundred pounds?—I should rather say that was my opinion.