Explanatory Notes, &c. By Prof. W. A. Bogers. 19 



after being ruled, the plate presented a most beautiful appearance 

 under a low power. 



No. 8. The lines of this plate are filled with graphite. The 

 peculiar mottled appearance of the glass will be at once noticed. 

 With glass of this quality I have ahvays obtained lines which fill 

 perfectly with graphite. 



No. 9. The observer is requested to examine the lines at the 

 end of the band nearest the star on the label and to determine 

 approximately the number of lines to the inch before examining 

 the other end of the band of which the fifth and tenth lines are 

 longer than the others. 



Third Series. Bulecl in 1883-4. 



No. 1. A very remarkable action of the diamond. 



No. 2, Varying pressure of diamond. Examine the very heavy 

 chips thrown off at the end of each line. 



No. 3. The only specimen of this peculiar action of the dia- 

 mond ever obtained. Attention is called to the form of mounting 

 which was here employed for the first time. The small hole in the 

 edge of the metal ring allows a free circulation of air and absolutely 

 prevents sweating.* 



No. 4. This plate followed No. 3 with a slightly greater pres- 

 sure of the diamond. There is a little dust between the plates. 

 In fact, several of the plates are defective in this way, but upon the 

 very rare occasions on which these and similar specimens were 

 obtained, the sole and first object was to preserve the lines intact, 

 as soon as possible and without regard to minor defects. 



No. 5. Varying pressure of diamond. The fine lines superb, 

 but in some places a little wavy. 



No. 6. Examine the chips at the end of the heavy lines, also 

 the quality of the fine lines. 



No. 7. This plate will repay a careful examination as illustrat- 

 ing the action of the diamond similar to that in plate 9 of the first 

 series. 



No. 8. Upon the whole, the most remarkable specimen ever 

 obtained. This plate, like No. 7, will bear a most careful study. 



No, 9. Illustration of a local explosion. In this case the 

 explosion took place at least one month after the lines were ruled. 

 It is not known exactly when it occurred. 



No, 10, Varying pressure of diamond. It will be seen that 

 the slight rubbing of the surface has in some places disturbed 

 the straightness of the fine lines. 



No. 11, Varying pressure of diamond. Fine lines good. 



* I am not quite sure of this statement. Oct. 1883. — W. A. R. 



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