May S-:, 1SS5.] 



♦ KNOV/LEDGE 



433 



NOBERT'S RULIXG MACHINE.* 



By Joun MAY.U.L, Jvx., F.R.M.S., F.Z.S. 



THE ruling machine of the late Herr F. A. Nobert, 

 which I have the honour to bring to your notice this 

 evening, in so far as its special applications for the produc- 

 tion of microscopical test plates, interference-plates, and 

 diffraction gratings are concerned, must, I think, be 

 regarded as of essentially original design. I have not been 

 able to connect its origin with any ruling machine of 

 anterior date, though I have searched somewhat diligently 

 through sundry journals and transactions of various socie- 

 ties, and have had the assistance of Dr. Hugo Schroder, 

 who is well known to have taken much interest in hue 

 mechanism, and more especially in Kobert's work, during 

 the past thirty years, and who has sought to inform himself 

 from every available source. 



I may at once state that, without the co-operation of 

 Dr. Schroder, my notes on Nol)ert's machine would have 

 been far less complete than they are ; and I must, there- 

 fore, at the outset, acknowledge my obligations to him 

 for many explanations and conjectures, without which 

 several important points of the construction would have 

 baffled me. 



I should also premise that Herr Nobert was extremely 

 reticent as to the methods he employed in the production 

 of his nilings. So far as I have been able to learn, he did 

 not fully communicate his methods to any one competent 

 to convey the information to others. The description, 

 therefore, which I shall present to your notice will consist 

 almost wholly of notes made by Dr. Schroder and myself, 

 after minutely examining every part of the machine, 

 together with a few gleanings from the memorandum-book 

 in which Herr Xobert jotted down, from time to time, 

 fragmentary observations and data, hardly to be understood 

 by any one but himself. 



But, first, for the information of those of my hearers who 

 may never have heard of Nobert's rulings, permit me to 

 make a few introductory observations as to the meaning 

 and purpose of fine rulings, so as to lead up gradually to a 

 comprehension of the problems which Nobert set himself to 

 solve, and the methods he adopted towards their solution. 

 In this way I hope not to have to draw too much on your 

 imaginations when I come to speak of the ditficulties of his 

 work, of the mechanical resources he developed in grappling 

 with these difficulties, and of the success he attained. 



I have here an ivory scale divided to hundredths of an 

 inch, the divisions of which are filled with wax and graphite, 

 so that the lines appear black and the interspaces white. 

 Every one present, who has normally good sight, will have 

 no difficulty in resolving the lines, that is, in seeing by the 

 unaided eye the spaces between the consecutive lines, pro- 

 vided the scale be suitably illuminated. Those smong you 

 who not yet tried the experiment will be surprised to 

 observe how much more perceptible are the lines if illumi- 

 nated by a condenser. If ivory scales were accurately 

 ruled, so that each line was equal in breadth to the inter- 

 space, some of you would resolve, without much difficulty, 

 lines as high as 1-50 to 200 to the inch with the unaided 

 eye, whilst here and there exceptionally powerful sight 

 would resolve lines even closer. These figures would be 

 slightly augmented if the lines were ruled on glass, and 

 viewed under the most favourable circumstances by trans- 

 mitted light. I have met with one instance where lines on 

 glass, slightly closer than 2.50 to the inch, were resolved by 

 the unaided eye. 



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

 the Society on May 6. 



I would here call your attention to a point which has 

 frequently produced niisundorstandings in discussions 

 relating to the possibility of perceiving fine lines. Ii» 

 referring to the resolution of lines, I mean the capacity of 

 separating, in vision, adjacent lines, that is, the recognition 

 of the interspace. This resolution must not be confounded 

 with the capacity of mere perception of a line or point, that 

 is, the recognition of the minimum visibilc. Many experi- 

 ments have been devised with a view to dctormiiiing the 

 conditions and limits under which the eye resolves lines or 

 points of interspace of a given fineness, but the problem has 

 not been absolutely solved, so far as I am aware. Neither 

 have the con4itions or limits under which the eye may 

 reach the ininimiini visibilc, — the perception of a line, or 

 point, in an otherwise homogeneous field of view — been 

 worked out with any approach to demonstration, for it 

 still remains to be explained under what optical and 

 physiological laws we are able to perceive stars which do 

 not subtend an appreciable angle, even to our finest optical 

 and measuring appliances. 



I have here a series of stage-micrometer rulings on glass, 

 commencing with fifty to the inch, and progressing to 

 10,000 to the inch. They probably belonged formerly to 

 the possessor of a microscope in the days when the measure- 

 ments of objects were generally made by direct inspection 

 and comparison under the microscope, and before the intro- 

 duction of the modern methods of measuring by screw- 

 micrometers, either on the stage or in the eye-piece. These 

 old rulings are of fair quality, and I show them with a view 

 of fixing in your minds a standpoint from which the fine- 

 ness of Nobert's rulings may be appreciated. 



Early in the century, Frauenhofer gave a great impetus 

 to fine rulings by the production of his diffraction gratings, 

 in which he aimed at and achieved a standard of accuracy 

 in division and perfect similarity as to depth, breadth, and 

 symmetry of angles of the furrows, such as had never 

 before been formulated. He succeeded in ruling lines 

 much clo.ser than those contained on the highest of the 

 series of micrometers I exhibit — as high, indeed, as 30,000 

 to the Paris inch ; but, according to Sir John Herschel,* 

 these fine lines were not sufficiently accurate to produce 

 pure spectra, nor could he go beyond 8,200 lines to the 

 inch when they were submitted to this most searching test 

 of accuracy. Sir David Brewstert mentions that Barton 

 produced rulings on steel up to 10,000 to the inch, which 

 gave excellent spectra in his hands. Some of you probably 

 have seen the so-called " Barton's buttons," which were 

 stamped from his ruled steel dies. 



{To he continued.) 



CHAPTERS ON MODERN DOMESTIC 

 ECONOMY. 



XXYIir.— THE FRAMEWORK OP THE DWELLING-HOUSE. 



STRUCTUEAL EXAMPLES (continued). 



THE DISPOSAL OF HOUSEHOLD REFUSE. 



IN the closing paragraph of our last communication, we 

 noted that the majority of closet appliances now in 

 the market, and constructed upon what Ls known as the 

 " wash-out " or " flush-out " type, are defective in two 

 important particulars. They retain too little water within 

 the basin, and the necessarily lateral position of the outlet 

 requires a very powerful flush to operate at all success- 

 fully. These difficulties have, however, been overcome at 



* Art. " Light," " Encyclopaedia Metropolitana," p. 489. 

 t " OpticB," " Lardner's Cyclopajdia," p. 120. 



