AW. 8, 1883] 



NA TURE 



This leads us to notice the Watt Rconi, or attic 

 workshop of James Watt, which still remains at Heath- 

 field Hall precisely as he left it — his lathe and bench 

 standing at the window, his tools lying about, and his old 

 leather apron hung on the vice. There are numerous 

 shelves with drugs and parcels on them, chiefly relating 

 to his invention of copying-ink, and nests of small drawers 

 full of tools ; but the principal objects which strike the 

 attention are two large machines for copying sculpture, 

 whether in marble, alabaster, or wood. One of them 

 copies to the exact size of the original, but the other is a 

 reducing machine, taking a copy on a very reduced scale. 

 The construction of both machines is described in the 

 paper, and bears testimony to the inventive and mechani- 

 cal genius of James Watt. The principle in each case 

 consists in using a bar or slide, having at one end a blunt 

 point to feel over the surface of the model, an"! at the 

 other end a quick-running drill to cut away the surface of 

 the material operated on. This drill is worked by a light 

 cord attached to an ordinary foot lathe, whilst the bar, 

 by means of a skilful arrangement of trussed frames, is 

 made movable in any direction as the feeler passes over 

 the model. The model and work can also be rotated, so 

 as to be set at an angle for handcutting, &c. The drills 

 and cutters, of which a large number are preserved, are 

 excellent in their design and workmanship. These ma- 

 chines were apparently the amusement of Watt's late 

 years, and are frequently referred to in his correspond- 

 ence. They were never protected in any way, and partly 

 perhaps for that reason have never been followed up and 

 brought to perfection. 



The second paper read was a report by the Research 

 Committee on Friction. The Institution experiments on 

 friction, which have been long delayed, have at length 

 been carried so far as to admit of the publication of an 

 interim report, prepared by Mr. Beauchamp Tower, 

 which proves to be of great interest. They are, properly 

 speaking, experiments on lubrication, being conducted on 

 a 6-inch steel shaft or journal, which could be run at any 

 given velocity, and on which rested a brass bearing 

 carrying a loaded frame. By altering the load on this 

 frame the pressure per square inch on the brass could be 

 altered ; and the temperature could also be altered by 

 means of gas jets under the journal. ."Xs a standard of 

 comparison experiments were first tried with the under- 

 side of the journal running in a bath of oil, so as to give 

 the maximum of lubrication. The results of these experi- 

 ments were to show that the friction of bearings under 

 such circumstances follows the laws of liquid rather than 

 (as usually assumed) of solid friction. These laws are 

 very different. Solid friction varies directly as the pres- 

 sure per unit of area, is independent of velocity at low 

 speeds (Morin), but decreases with increasing velocity at 

 high speeds (Gallon, &c.). Licjuid friction, on the other 

 hand, is independent of the pressure per unit of surface, 

 is directly dependent on the e.xtent of surface, and in- 

 creases as the square of the velocity. In fact it is not 

 friction at all, but the shearing of one part of a more or 

 less viscous fluid across another, as the above law 

 plainly indicate. Now the Institution experiments show 

 that, in the case of oil-bath lubrication, there is really a 

 film of liquid oil surrounding the journal and keeping it 

 away from the brass ; and that what is called journal 

 friction is really the shearing of one part of this film over 

 the other. In such cases the friction may be exceedingly 

 small : in some of these experiments it actually was as 

 low as l/iooofh, and i/jooth is easily attained. This is 

 much below what is generally supposed to obtain. The 

 limit of pressure appeared to be about 600 lbs. per square 

 inch. Beyond this the oil is squeezed out, and the metal 

 " seizes." This is of course with high speed and constant 

 pressure ; with low speeds and intermittent pressure (as 

 was pointed out in the discussion) very much higher 

 pressures are admissible. 



So far the experiments were satisfactory ; but when 

 the oil-bath was replaced by ordinary modes of lubrica- 

 tion, great difficulties were experienced. When the oil 

 was introduced from above through grooves in the brass, 

 it was found that, however these were cut, and at what- 

 ever part of the brass then opened, the bearing seized at a 

 comparatively low pressure. The fact that such methods 

 do as a matter of fact answer with ordinary railway 

 vehicles is accounted for, it is supposed, by the end play 

 of such bearings, and probably also by the general vibra- 

 tion. When, however, a pad fed with oil by capillary 

 attraction from a bath below, was placed below the 

 journal, so as to press lightly against it, satisfactory 

 results were obtained, although the lubrication was so 

 slight as only to appear to the touch as a slight greasi- 

 ness. The laws here, however, approximated to those of 

 solid friction, and probably the oil merely acts to fill up 

 the little inequalities of the metal, and so practically 

 render it smoother. 



A curious subsidiary result should be noticed. When 

 the oil-bath experiments were in progress, advantage was 

 taken of the brass being removed to drill a hole in it 

 for the subsequent tests with ordinary lubrication. On 

 resuming the running, however, the oil was found in the 

 hole, and on a pressure-gauge being attached, the finger 

 rose to above 200 lbs. per square inch, which was 

 the limit of its indications. This pressure was above 

 the average pressure on the brass, and shows clearly that 

 the surfaces are separated by a continuous film of oil, 

 having at each point an actual hydrostatic pressure due 

 to the external pressure which obtains at that point. 



C)n the whole, these experiments, while to a great 

 extent confirming the well-known researches of Prof 

 Thurston in America, throw a good^deal more light on the 

 curious phenomena and laws of journal friction. Their 

 results (including some on temperature, which was found 

 to have a marked influence in diminishing friction) are 

 contained in a series of tables, which our space forbids us 

 to publish, but which can no doubt be obtained, by any 

 one interested, from the offices of the Institution, at 16, 

 Victoria Chambers, Westminster. 



NORDENSKJOLUS GREENLAND 

 EXPEDITION'' 



II. 

 T N my report of the expedition of 1870 I drew attention 

 ■'- to a clayey mud which is found in circular cavities, from 

 one to three feet in depth, on the surface of the inland 

 ice, not only near the shore, but even as far inland as we 

 reached on that occasion. My companion on that occa- 

 sion, Prof. Berggren, discovered that this substance 

 formed the substratum of a peculiar" ice-flora, consisting 

 of a quantity of different microscopical plants (algae), of 

 which some are even distributed beyond the clay on the 

 ice itself and which, in spite of their insignificance, 

 play beyond doubt a very important part in nature's 

 economy, from the fact that their dark colour far more 

 readily absorbs the sun's heat than the bluish-white ice, 

 and thereby they contribute to the destruction of the ice- 

 sheet, and prevent its extension. Undoubtedly we have, 

 in no small degree, to thank these organisms for the 

 melting away of the layer of ice which once covered the 

 Scandinavian peninsula. I examined the appearance of 

 this substance in its relation to geology, and de- 

 monstrated : — 



I. That it cannot have been washed down from the 

 mountain ridges at the sides of the glaciers, as it was 

 found evenly distributed at a far higher elevation than 



^ Continued from p. 13. 



= Lately described by Prof. V. Wittroclc. " Om Snons och Isens Flora, 

 Sarskildt i Arktiska Traktema." Ur "A. E. Nordenskjiild, Studier och 

 Forbkningar foranledda af mina resor i hoga Norden." (Stockholm, 1883.) 

 See Nature, vol. .xxviii. p. 304. 



