PROCEEDINGS OF THE SOCIETY. 379 



He believed that Herr Nobert's earlier rulings were upon artificially 

 prepared surfaces on the slips themselves, and that later on (about 

 1860) he came to the conclusion that the melted surface of cover- 

 glass was better for his test-plates. Subsequently Dr. Schroder 

 instructed him in a method of polishing the " mild " glass, which 

 induced him to revert to artificial surfaces again. The later test- 

 pla.tes were probably all ruled on the prepared " mild " glass, thinned 

 down to suit high-power objectives. Mr. Mayall said he must defer 

 his remarks on the diamond points till the next meeting, now men- 

 tioning only that the ten diamonds that accompanied the machine pre- 

 sented varieties of preparation. Some had two worked surfaces brought 

 to a knife edge ; others one worked surface and one surface of fracture 

 meeting in a knife edge ; others had two surfaces of fracture meeting 

 in a knife edge. By reference to Herr Nobert's memorandum book, 

 Mr. Mayall said he hoped to be able to explain the character of the 

 diamonds which were noted as being successful. In conclusion, Mr. 

 Mayall said it was abundantly proved by Herr Nobert's work that 

 the perfection of the mechanical part of the dividing engine was not 

 the only difficulty which he had understood and conquered. There 

 was a still greater difficulty which he had understood, and which he 

 had met with a success that gave him pre-eminence in this depart- 

 ment of micro-physics, and that was the preparation of the diamond 

 ruling points. 



The President expressed the thanks of the meeting to Mr. Mayall 

 for his description of a machine which exhibited such an immense 

 amount of commendable ingenuity in its construction. He thought 

 it must be a source of gratification to the Society to know that as the 

 machine now belonged to Mr. Crisp, they might hope at some future 

 time to hear more about it, and to see something of its performances. 



Mr. Crisp said that Mr. Mayall had kindly undertaken to describe 

 and illustrate the machine in a future number of the Journal. 



Mr. Beck said that a paper upon this machine, giving all the details 

 of its construction with illustrations, would be extremely interesting, 

 and he hoped that Mr. Mayall would not only describe its perfections, 

 but would also point out all its weak points, which were sometimes 

 even more interesting and instructive, as showing the manner in 

 which the inventor had been able by practice to overcome them. He 

 remembered that many years ago the micrometer ruKng machine by 

 Mr. Jackson produced in his hands some of the best work of its kind 

 that had then been seen ; but when after his death it passed into 

 other hands, some of the worst productions resulted. Mr. Jackson 

 had, no doubt, found out all its weak points, and had overcome them 

 by the exercise of his own manipulative skill ; and it would be very 

 interesting to know how Nobert had got over all his difficulties, so as 

 to be able to produce bands of lines which stood altogether unrivalled. 



Dr. Matthews inquired if there was any provision made for 

 dropping the point upon the plate on commencing a line ? 



Mr. Mayall said this seemed to be one of the weak points of the 

 machine, for it would be seen, on examination of the test-plates, that 

 there was frequently a small fracture at the beginning of a liue, and 



