504 



♦ KNOV\ALEDGE ♦ 



[June 12, 1885. 



length no longer visible ; but I have no doubt they con- 

 tinued falling for a considerable time after, and until the 

 atmosjjhere iecame rarefied h)j the sun's rays. 



It will here, perhaps, be proper to give some account of 

 the state of the weather, and of the atmosphere imme- 

 diately preceding and during the above event. The period 

 when this phenomenon occurred was what is called in 

 America " the Indian summer," which generally begins in 

 the early part of November, and continues for one or two, 

 or even three weeks, during which time the weather is 

 perfectly calm and warm both by day and by night, with a 

 hazy, smoky appearance in the daytime ; and in the after- 

 noon of the 12th there fell a light, gentle rain, which lodged 

 like dew on the grass, and continued for about half an 

 hour, after which it cleared up, and presented a calm, clear, 

 warm, starlight night. On the morning of the observation 

 I laid my hand on the bare ground, which felt compara- 

 tively warm, and on looking at my thermometer found it 

 standing at 66° Fahr. ; but as I had no barometer I can- 

 not state what the pressure of the atmosphere was. The 

 above observations were made on a farm about six miles 

 north-west of Baltimoi-e, and upon conversing with others 

 on the subject I learnt that the phenomenon extended 

 southward all over the State of Virginia, where it was 

 still more brilliant, and north-eastward to Philadelphia, 

 where it was fainter, but was not visible at New York ; for 

 going to the latter city a few days after I made many 

 inquiries, but could iind no one who had either seen or 

 heard anjiihing of it. 



In one of the accounts I read some attempt is made to 

 count the number of stars, as they are called, that fell ; 

 but from what I saw it would be as easy to count the 

 number of flakes of snow or hail-stones during a moderate 

 fall. 



NOBERT'S RULING MACHINE.* 



. Br John Mayall, Jun., RR.M.S., F.Z.S. 



(Continued from p. 4tJ3.) 



HAVING given you a general view of the meaning and 

 purpose of the tine rulings produced by Herr Nobert, 

 I proceed to the description of the ruling-machine itself, 

 and of the methods he probably employed. 



The foundation of the machine is a dividing engine, 

 calculated to produce parallel divisions far finer than could 

 be marked by any ruling point yet discovered. The 

 division-plate is about 12 in. in diameter, and has twenty 

 rows of " dots," by means of which two bands of silver 

 embedded near the circumference have been graduated 

 with extremely fine lines to every five minutes in arc. 

 These gradations are viewed by two compound microscopes, 

 each provided with eyepiece screw-micrometers of special 

 construction. The microscopes can be fixed at various 

 points on the edge of the main iron bed of the machine, 

 so as to check the rotation of the graduations of the 

 division-plate ; and the eye-piece screw-micrometers in 

 the microscope enable the observer to subdivide the 

 graduations by inspection, and to correct the move- 

 ment of rotation, within very narrow limits. The 

 rotation of the division-plate is etiected by a tangent-screw 

 acting upon a worm on the edge of the division-plate. The 

 tangent-screw is controlled by a large milled head, and a 

 graduated drum shows the amount of motion. A screw 

 adjustment is provided, by which the tangent-screw can be 

 disconnected from the division-plate. In order to equalise 

 the pressure of the tangent-screw against the division-plate, 



* From the Journal of the Society of Arts. A paper read before 

 the Society on May 6. 



It is mounted to swing between conical bearings, and a 

 counterpoise on a lever arm beneath keeps It in contact 

 with the worm. The method employed by Nobert for 

 obtaining the minute divisions of his test-plates was, to 

 utilise the radius of the division-plate as a lever to move 

 the glass plate on which the rulings were made at right 

 angles to the motion of the ruling point. For this purpose, 

 he attached to the centre of the division-plate a bent 

 arm, on which slides a bar faced with silver, having 

 at one end a finely-polished steel point which can 

 be adjusted by a scale and vernier so as to project 

 more or less beyond the centre of the division-plate 

 or axis of rotation. The radius of the division-plate 

 thus becomes the long arm of the lever, whilst the radius 

 of the projection of the polished steel point beyond the axis 

 of rotation forms the short arm, the centre of the division- 

 plate being the fulcrum. The motion of the short arm of 

 the lever is communicated by contact with an agate plate 

 to a polished steel cylinder, adjusted to slide at right angles 

 to the movement of the ruling point in V-shaped bearings 

 of agate. The steel cylinder carries a circular metal table, 

 on which the glass plate to be ruled is fixed by wax and 

 clamps. To diminish the friction of the steel cylinder on 

 the agate bearings, a counterpoise is provided, to lift it on 

 a roller, whilst a weight, attached by a silk cord to one end, 

 keeps the agate plate in perfect contact with the motor 

 steel point. The motion of the lever arms is, of course, in 

 arc, and hence the division would not be strictly equidistant 

 unless compensation were made for the difference in length 

 of the arc and its sine ; but smce the actual space included 

 between the first and last lines of the test-plates hardly 

 exceeds l-50th inch, this diflerence would be inappreciable. 

 It may be assumed that Herr Nobert used the arc motion 

 during the process of division only, and that for moving the 

 plate over the spaces of the blank bands between the 

 rulings he utilised the fine screw connected with the agate 

 plate in the steel cylinder, by which a motion of 

 the plate of about -joVo ^^ ^^ vach. can easily be 

 efi'ected ; in this way he would reduce the total motion of 

 the division-plate in arc to about one-half. It would be 

 possible to increase or decrease the successive divisions of 

 the bands by increasing or decreasing the length of the 

 short arm of the lever ; but, in view of the risk which such 

 adjustments would involve, it is highly improbable that 

 such a plan was adopted. There are other possible methods 

 of eflfecting the divisions, all involving risks of large errors ; 

 the most probable conjecture is that Herr Nobert used the 

 greatest possible excentricity of the short arm of the lever, 

 so as to utilise the smallest motion in arc required for his 

 subdivisions. 



The arrangement for carrying and adjusting the diamond 

 point is specially ingenious. The questions to be solved 

 were — (1) to provide means to adjust a diamond edge to 

 any angle within required limits ; (2) to balance it truly, 

 so that the weight-pressure for ruling could be perfectly 

 controlled ; (3) to raise and lower it strictly in one plane — 

 that is to say, mechanically free from lateral play, so that 

 the consecutive divisions of the ruling depended solely on 

 the motion imparted to the glass plate by the dividing 

 engine ; (4) to cause the diamond to oscillate freely in one 

 plane ; (5) to control the length of the lines to be ruled ; 

 (0) to connect the whole with mechanism to insure an even 

 rate of speed in the ruling movement of the diamond. 



These matters have been worked out by Herr Nobert 

 with extraoi'dinary perseverance, as is evidenced by the 

 elaboration of the adjustments. I should despair of 

 making myself understood on these points by mere verbal 

 description ; I shall, therefore, ask you to inspect the 

 mechanism at the close of my remarks, for, to be under 



