Important Standard Yard Measures. 51 



the Treasurer of Tasmania, the bars were brought to Melbourne, 

 and the inter-comparison was carried out by me at the Mel- 

 iDOurne Observatory during the months, June-November, 1918. 



The New South Wales bar. No. 18, Standard at 62.26° R, 

 was found when examined at the Melbourne Observatory to be 

 in good condition, a few spots only appearing on the main por- 

 tion of the bar, and the lines on the gold pins were very good. 

 The Tasmanian bar, No. 37, Standard at 62.07° F., appeared 

 in good condition as regards the outer surface, but on examin- 

 ing the lines under the microscope, those on the left hand plug 

 were found to be fearfully scraped and utterly ruined; the. only 

 part for pointing on is at one end of the terminal line, outside the 

 longitudinal lines. In the comparisons, pointings on the other ter- 

 minal line were made at about the same distance outside the 

 longitudinal lines, but evidently the original comparison of the 

 "bar cannot be used. 



In the meantime the comparator to be used had been im- 

 proved and had been given its final form, the micrometer screws, 

 investigated, and revolution values determined. The two micro- 

 scopes used were supported in heavy cast iron stands which 

 rested on a massive slate slab on stone piers isolated from the 

 floor, the whole forming a most stable system. The microscopes 

 can be raised and lowered, and the optical axis made vertical by 

 three adjusting screws and lock nuts. The illumination is most 

 important. A small electric lamp was fixed to the microscope 

 tube a little above the objective. The light from it passed 

 through a hole in the tube on to a cover glass inclined at 45° 

 to the vertical, and thus the light was thrown vertically through 

 the objective on to the line on the bar. This arrangement gave 

 a good illumination. It could be somewhat improved by inter- 

 posing a lens between the lamp and the hole in the tube, thus 

 •enabling the lamp to be moved further away. The lamp was 

 rswitched on only while the pointing was being made. 



Two girders were bolted across from pier to pier, and on 

 these were supported the rails on which the heavy wooden 

 moving table ran. Cast iron tables, planed on the upper surface, 

 three ins. wide and 48 ins. long, were supported near the ends 

 1)y strong screws, fixed firmly into iron castings screwed to the 

 moving table. These screws served for raising and lowering the 

 cast iron table through a range of three inches. There were 

 two of these tables side by side separated by a space of one inch* 



