Micro-ruling on Glass and Steel. 155 



and Powell and Lealand's modification of Professor Smith's vertical 

 illuminator for high powers, the complex portions of the pattern are 

 resolved, but with decided suggestion that the cuts are elevations, or 

 threads laid upon a semi-transparent surface like white porcelain. 



There is an advantage in studying the appearances that can be 

 obtained with objects of this description, because the illusions can be 

 corrected by higher powers and various modes of managing the 

 light. They suggest causes of misinterpretation, and may thus 

 prevent mistake, and the objects which are of great beauty illus- 

 trate a variety of diffraction effects. 



On showing Mr. Stanistreet's exquisite work to several friends 

 well acquainted with dehcate mechanical operations, the remark has 

 uniformly been. He must have costly and complicated apparatus to 

 produce such results ; but in reply to my inquuies, he writes, " My 

 little ruling machine is a very homely and inexpensive aflfaii', having 

 been planned by myself, and constructed entkely by my own hands 

 of such materials as came within my reach — crinoline wire, broken 

 watch-springs, copper coins, and the heads of carpet pins, with some 

 pieces of brass and steel, forming the entire structm-e." He adds 

 that " the machine consists essentially of two separate parts : the first 

 for giving equable motion to a minute fragment of diamond • bort ' 

 set in the cleft of a piece of softened brass wire. This point is 

 moved by a very fine steel screw of 100 threads per inch, which I 

 made as perfect as my means admitted, and it moves the diamond 

 through the agency of a simple lever toVo^-^ ^f an inch for each entire 

 rotation of the screw." 



" The disk of glass to be engraved is suspended over the diamond 

 by a spring (crinoline wire), and is made to move across it by a 

 revolving coin — a penny-piece, having an inchned plane of thin 

 brass soldered to one-half its chcumference — and this, when rotated, 

 raises and develops the glass disk very gently, di-awing it across 

 the diamond thi'ough a space hmited by adjusting screws, letting 

 down the glass very gently and hfting it off suddenly at the end of 

 each half revolution of the coin." 



Mr. Stanistreet works very quickly with this machine. He is 

 able to rule 100 paraUel lines from 1—1000" to 1—10000" apart 

 in one minute of time, but, as may be supposed, does not attempt 

 very delicate work at such a pace. The complicated star last 

 described — an exquisite specimen of delicacy and skill — occupied 

 three hours and twenty minutes, which seems a short period for 

 such a number of lines and so comphcated a pattern. 



I should add that the preceding description applies to the machine 

 as first made. Before the specimens described were ruled, an addition 

 was made to the apparatus with a more delicate means of motion 

 than the screw. I am informed it would requn-e accurate drawings 

 to make the structure intelhgible. Mr. Stanistreet informs me that 



