390 
Transactions of the Society. 
0*7626 in. plug, the exact standard screw as originally suggested 
could be adhered to. These adjustable taps and dies were not used 
for cutting the thread, but for passing over each thread after it had 
been cut to approximately the right size. That this method will work 
satisfactorily, is evidenced by the fact that in the late Mr. Eichard 
Beck’s firm the method has been in successful operation ever since. 
The use, however, of such a system involved the necessity of 
every maker being provided with adjustable tap and die, and also the 
two pairs of plug and ring Whitworth sizes, together with a means of 
accurately sharpening the adjustable tap and die. And it was found 
in practice that Microscope makers were not universally prepared to 
go to such an outlay for a matter which at that time did not appear 
to be of such importance as has since proved to be the case. 
Therefore the Society issued solid taps, and finding that, as is 
well known to be the case, a solid tap could not be made to an exactly 
accurate size owing to the alteration of the steel during the process of 
hardening and tempering, they had them made somewhat larger than 
the standard 0*8 in. gauge. An additional reason for their being 
larger was to allow for the slight wearing of the tap after prolonged 
use. 
Here, however, there was no record of the amount larger which 
the taps were made, and although the first set appear to have been care- 
fully manufactured, those which were from time to time obtained were 
less and less like the original, and in this manner a discrepancy arose 
which the arrangements now adopted by the Council are intended to 
correct for the future. 
Beyond the fact that the Council specify that the diameter of the 
plain fitting of the object-glass should be as near as possible to, but 
not exceeding 0*759 in., and that the length of this fitting has been 
reduced to 0 * 1 in., the original specification of the standard screw is 
only altered as to the exact diameters of the screw itself. 
The original specification of these diameters allowed only 0*0018 
for clearance between the male and female screw. 
If absolutely exact sizing taps and dies could be made which 
should not wear, the original diameters might have been adhered to, 
but as has been previously pointed out, adjustable dies in connection 
with gauges, &c., are requisite for this. 
The Council has been able to obtain taps and dies which are 
guaranteed not to vary more than 1/1000 of an inch larger or smaller 
than the nominal size. And they are therefore having manufactured 
a series of taps of the nominal diameter on the top of the screw- 
thread of 0*8015 in. which will not vary more than from 0*8005 
in. to 0*8025 in. To ensure this the Council has ordered a Whit- 
worth plug and ring, size 0 * 803 in. in diameter, and no tap will be 
allowed to be stamped with the Society’s stamp unless it will pass 
easily through this 0 * 803 in. ring, and unless it is of such a size 
that it will not enter the 0*8 in. standard gauge already in the 
Society’s possession. 
