130 SUMMARY OF CURRENT RESEARCHES RELATING TO 



2. The greatest difficulty encountered in setting a ruling crystal 

 is to obtain one wliicli will rule lines of tlie required quality whicli 

 will retain their form after the surface of the glass is rubbed. The 

 crystal with which nearly all the plates of this series were ruled was 

 only obtained after a search continued at intervals through several 

 weeks. Sometimes a diamond which will rule good light lines will 

 not produce good heavy lines, and vice versa. According to my 

 experience it is better to have a special diamond for each class of line 

 desired, though the diamond with which the present series of plates 

 was ruled seems well adapted to every kind of work required, except, 

 perhaps, the production of the finest bands. An examination of 

 plates illustrates the wide difference in the character of lines ruled 

 with the same diamond, after the edges of the ruling crystal have 

 been worn smooth. In one there are two sets of lines, side by side, 

 in one of which the surface has been rubbed, and in the other of 

 which the lines have been left undisturbed. The difference is very 

 marked. It may be said here that the surface of a ruled plate should 

 always be cleaned by rubbing in the direction of the lines only, never 

 at right angles to the lines. It will often happen after sharp rubbing 

 that the lines appear ragged, when the difficulty is that the chips 

 have not all been removed from the grooves. Rubbing with Vienna 

 lime, moistened with alcohol, will usually complete the cleaning 

 satisfactorily. 



3. After a crystal has been found which will fulfil the con- 

 ditions of producing a line which will bear cleaning, there still 

 remains a difficulty which will only be revealed after the lapse of 

 considerable time. This is well illustrated in one plate in which 

 the lines were as perfect as could be desired for several days after 

 they were ruled. The lines of the band are now completely broken 

 up. Evidently they were in a state of strain, which finally became 

 so great that resistance to rupture became impossible. This, how- 

 ever, is an extreme case. Generally the lines simply enlarge at 

 certain points. Usually the termination of the enlargement occurs at 

 irregular distances along the lines, and it is nearly always very 

 sharply defined. The most curious action of this kind which has 

 ever come under my notice is where the lines have broken up into a 

 form something like the strand of a heavy rope. 



The process of setting a diamond is as follows : The holder has 

 the means of adjustment in three planes : {a) an adjustment in a 

 horizontal plane ; (h) an adjustment in a vertical plane ; (c) an ad- 

 justment in a plane at right angles to the ruled lines. It is my 

 practice to begin by giving the knife-edge of the diamond consider- 

 able inclination to the line of motion of the ruling slide. I then rule 

 a series of single lines at different known angles of inclination, care 

 being taken to pass the line of parallelism. An examination of the 

 character of the lines thus ruled will enable one to determine within 

 narrow limits near which one the knife-edge is set parallel with the 

 glide. After a fair line has been obtained in this way a sharp crystal 

 is generally found by tilting the diamond in a vertical plane, though 

 it will often be found necessary to make the third adjustment men- 



