448 
LIEUT. -COL. A. E. CLAEKE ON STANDAEDS OE LENGTH. 
nicated to the cast-iron microscope-holders. In order to remove this possibility a new 
form of candle-holder was introduced, which does not come into contact with the cast- 
iron plates, and admits of being very easily adjusted to the proper position from time to 
time. Some improvement has been also made in the apparatus for measuring calibration 
errors of thermometers, and also (mainly by increasing the quantity of water) in that for 
comparisons of thermometers. 
The values of one micrometer-division of the microscopes H and K obtained in 1863 
were 
£=0-79494+0-00008, 
£=0-79800 + 0-00009 ; 
in 1865, 
£ = 0-79566+0-00008, 
£=0-79867 + 0-00009. 
In 1869 the values were determined again with the result, 
£=0-79564+0-00010, 
£=0-79837+0-00010. 
Two new micrometer-microscopes marked I and J have been added to the apparatus. 
They are longer than Ii and K ; the distance from the object observed to the object- 
glass is 4 inches, from the object-glass to the micrometer-threads 14-6 inches. The 
value of one division of either of these microscopes is very little different from that of 
one division in the microscopes H and K. They were determined from ten measure- 
ments of the same space, giving it equal to 1368-457 or 1381-50+ where 7 and j represent 
the values of one division in the respective microscopes. From these measures we get 
7=0-81032+0-00018, 
+=0-80270 + 0-00015. 
These microscopes have never been used for any large measurements, and the values 
are therefore sufficiently precise. 
The space between the lines on the contact-apparatus has been repeatedly examined, 
and appears to be as nearly as possible invariable. The results obtained from very 
numerous comparisons in different years are : — 
In 1863 
„ 1864 
„ 1865 
§=565*62, 
£=565-55, 
£=565-69, 
£=565-64. 
1869 
