ducing the testimony of writers on mechanics, who, guided by these results, had promulgated the laws deduced from them. He gave quotations from the following authors in corroboration of his views, viz.-Emerson, Playfair, Tredgold, Barlow, Lardner, Farey, De Pambour, Poisson, Pratt, Whewell, and Mosley. With the last mentioned author Mr. Pole had taken an opportunity of conversing upon the points in question, and the principles adopted in the paper had received the Professor's full approbation, as corresponding with those made use of in his own treatise.

Mr. Vignoles thought that great praise was due to Mr. Pole, for the research and mathematical reading exhibited in treating the question of comparative friction. In the former remarks he had made, it was not his intention to impugn the accuracy of the abstract proposition, "that friction was independent of the area of bearing surface," any further than to qualify it in its practical application, with the proviso, "that proper proportions were maintained between the area and the pressure, according to the description of mechanism, subjected to friction." He therefore desired to consider the question, as to how far, in practice, one kind of engine varied from the other in the general amount of friction, and to examine how far the areas of the bearing surfaces were in proportion to the insistent weight, caused either by the strain of any angle, or by the direct weight on any of the journals of the moving parts; this inquiry should precede the abstract mathematical investigation. The friction of different substances would not follow the mathematical rule, unless the due proportion between area and pressure was ascertained and observed; these proportions would be very different in heavy machinery, such as marine steam-engines, and the axles of railway carriages. With these qualifications he agreed with the general propositions laid down by Mr. Pole.

Mr. Murray agreed with Professor Vignoles in thinking that the extent of surface in machines materially affected, in practice, the amount of the friction.

He did not mean to advocate the correctness of Professor Vince's experiments, but he would draw attention to the results quoted by Dr. Gregory, in which the difference of Vince's experiments and those of other writers on the subject, was attributed to their not taking into account the cohesion of the bodies experimented upon. Their experiments were made with inclined planes, which were raised until the bodies began to move, and

the amount of friction was then deduced from the angle of inclination that had been given to the plane: from this mode, it was contended that no definite laws could be laid down.

Mr. Murray acknowledged that on dry surfaces, within certain limits, the amount of friction was not influenced by the extent of surface; but he contended that in practice, as different kinds of unguents were used, the cohesion arising from the impurity and clamminess of these lubricating substances, must be considered and allowed for.

Major-General Pasley said that when he was quartered at Malta, he tried some experiments on friction, by having a slab of Maltese stone, which resembled the oolite of Bath, rubbed smooth and placed horizontally; other pieces of smooth-faced stone of the same quality, but of different areas, were then attached to a cord which was weighted and passed over a pulley; the weights, which were just sufficient to give motion to the several pieces of stone, were then noted, and it was found that the area of the surface was not important, the friction being directly in proportion to the insistent weight of the stone. He could therefore corroborate Mr. Pole's propositions.

Mr. Farey considered that Mr. Pole had treated the subject of friction so well, and had selected his authorities in such a manner, as to establish his position incontrovertibly; he would therefore only remark, that in collating the friction experiments for his work from Dr. Gregory and others, he had in a measure rejected those of Vince, as being on too small a scale, and not of sufficient importance to rely upon as authority.

It must be admitted, that viewing the question practically, there were circumstances which would influence the proposition. If the surface of a journal was so small as to drive out the unguent, or to cut into the lower bearing, the friction would be unduly increased, and the theoretical position would no longer hold good. The use of unguents would not interfere with the general proposition, although in practice, any substance used for lucubration, which, when cold, solidified and became adhesive, might, for a time, produce an increase of friction; this of course would be avoided, but it would not bear upon the general question.

Mr. Rennie corroborated the position assumed by Mr. Pole, "that friction was independent of the extent of the rubbing surface:" his experiments, which had been tried on a large scale, and with various substances, gave uniformly this result, within

the limits of abrasion : when that commenced, the bearings heated and there was an end of the theoretical position. The texture also of the rubbing surfaces altered the condition; for instance, any light body covered with cloth opposed a considerable resistance by the friction of the raised nap; but if the body was weighted, it again came within the limits of the law, because it more nearly resembled hard substances, which alone were considered in theory. Hard and soft woods varied, of course, in the same manner. The friction upon each other of metals of different degrees of hardness, caused in practice some little variation, but it was so slight, that the rule quoted, might be safely received as correct.

[To be continued.

POPULAR CYCLOPÆDIA OF NATURAL SCIENCE.*

PART IV.

In the present age, whilst works on all subjects are teeming from the press, and elaborate essays upon all branches of science are reduced to the consistence suited for feeding the minds of children, yet a gap in this kind of literature has been left, greatly to the detriment of those who have passed through the primitive "conversation books" on science, but are not sufficiently advanced to attack the, to them, formidable philosophical treatises which are held in the highest estimation. It was with no little pleasure that, on examining the present work, we found the author's intention was, as he stated in his prefatory notice, “to occupy a place somewhat intermediate between the simple elementary treatises on Physical Science and the more elaborate works of a professedly philosophical character."

The present Part contains an account of the gradual improvements in Horology, or the construction of instruments for the measurement of time, and also a display of the Science of Astronomy. Of the treatment of the former subject, which has principally engaged our attention, (the latter having met with less neglect at the hands of authors than most of the sciences,) we give our unqualified praise, both for the completeness of the

Published by W. S. ORR, & Co., Paternoster Row.

information communicated, as well as the lucid manner in which it is exposed. The author, in commenting on the necessity the early inhabitants of the world would naturally feel for dividing the day into regular portions of time, says, "various instruments were contrived for this purpose, and some of them shewed great ingenuity. The common hour-glass, in which the interval is measured by the passage of fine sand through a small hole, seems to have been one of the earliest of these."

"The most satisfactory of the ancient instruments for the measurement of time, was the Clepsydra, or water-clock, in which the hours were indicated by marks upon the side of a vessel, filled with water, from whose bottom a small stream was allowed to flow out. As the water in the vessel ran off, its surface sank, and its height, as shewn by the marks, indicated the time that had elapsed." After pointing out the defects of this construction of time-keeper, and the rude attempts made to correct them, the author proceeds to explain, by the aid of diagrams, the general principles on which clocks and watches are constructed. The important improvements are also clearly traced; the going-fusee, the improved as well as the simple escapement, the compensation balance and pendulum, and the complicated apparatus necessary for striking, are brought within the comprehension of the merest tyro in the mechanical art.

In concluding this notice of the Popular Cyclopædia of Natural Science, we cannot but congratulate the Publishers on their fortunate selection of the gentleman who has so well carried out the views they entertained, when commencing the publication of these treatises.

List of Disclaimers

OF PARTS OF INVENTIONS AND

Amendments

MADE UNDER LORD BROUGHAM'S ACT.

William Palmer,-disclaimer and memorandum of alteration to patent dated 9th November, 1841,* for "improvements in the manufacture of candles." Filed 16th March, 1843.

In the specification of this patent, which will be found at page 358, of the present Vol., four improvements are described; the patentee now disclaims all but the first.

William Lomas and Isaac Shimwell,-ditto to patent dated December 8th, 1842, for "certain improvements in the manufacture of fringes, cords, and other similar small wares, and also in the machinery or apparatus for producing the same." Filed 12th June, 1843.

Alphonse Réné Le Mire De Normandy, M.D.,-ditto to patent dated 8th September, 1841, for " certain improvements in the manufacture of soap." Filed 13th June, 1843.

List of Patents

Granted for SCOTLAND, subsequent to May 22nd, 1843

To Charles Maurice Elizee Sautter, of Austin Friars, London, for improvements in the manufacture of borax,-being a foreign communication.-Sealed 23rd May.

John Laing, of Dundee, linen manufacturer, for improvements in apparatus for rubbing linen cloth, when making in powerlooms. Sealed 23rd May.

John Nisbett, of Elm-street, Long-lane, Bermondsey, London, engineer, for improvements in preparing hides and skins in the manufacture of certain descriptions of leather.-Sealed 23rd May.

Joseph Burch, of the City-road, London, engineer and machinist, for certain improvements in machinery for printing on cotton, silk, woollen, paper, oil-cloth, and other fabrics and materials, and certain apparatus to be used in preparing the moulds and casting surfaces for printing, and for certain modes of preparing surfaces previously to the design being delineated upon them. -Sealed 23rd May.

Angier March Perkins, of Great Coram-street, London, engineer, for improvements in the manufacture and melting of iron, which improvements are applicable to evaporating fluids.-Sealed 25th May.

William Brown, of the city of Glasgow, for improvements in

the manufacture of porcelain, china, pottery, and earthenware; and which improvements are also, in part, applicable to the manufacture of paper, and to the preparation of certain pigments or painters' colors.-Sealed 26th May.