24 ON HIGH POWERS, AND A STEADY MICROSCOPE. 
last annual meeting, is rather startling after such a report, 
and, no doubt, several will disagree with it. Having for a 
a time worked with object-glasses of -',th and of 
;th power, and latterly with a ~;th (all most excellent ob- 
jectives, as many can testify), I venture to give my opinion 
on the point in question; still, differing from so eminent 
an authority as that of Mr. Brooke may be thought pre- 
sumption on my part; and I cannot but think, knowing S10) 
well the accuracy of Mr. Brooke’s observations, that his ath 
must have received some injury for a -},th, however good, to 
resolve difficult points of structure equally well with it. My- 
object-glass of .;th power works through thicker glass 
covering than my voth does; the poreacion for glass 008 
thick is only 8 to 10, it corrects to 36; up to 20 correction, 
the defining power is perfect; higher correction, that is, from 
20 to 36, takes away from the definition, still the objective 
will focus for covering glass almost as thick as the th will 
focus for. 
It resolves Pleurosigma angulatum into spherical elevations, 
as likewise Navicula rhomboides; it clearly shows that the 
wedge-shape markings on the Podura scale are not so many 
separate wedges, but a continued corrugated structure, giving 
strength to the extremely delicate scale; also the membranous 
tissue of the mouse-hair (if it may be so termed) is far more 
evidently seen with the 4th than with any other power. My 
_!,th of 150-aperture is a most excellent glass, well known to 
many members of the Microscopical Society, but it cer tainly 
does not define so clearly, nor elucidate so plainly, as the 
~th; the difference is marked. The th in question, of 
Mr. Thomas Ross, I have certainly not seen through, but a 
friend of mine, who witnessed its performance on two occa- 
sions, told me that, although it was a most excellent glass, 
he did not consider it better than my ;{,th, and certainly not 
to be compared with the }=th. 
In Extract III it is stated that the ;,th of Mr. Ross was 
an entire new construction; but in Extract II we are led to 
suppose that it was an old glass with one of the combinations 
new, admitting of a different correction; with the ‘th as 
altered Mr. Brooke and Dr, Beale worked; it does not, how- 
ever, appear that Dr. Beale coincided with Mr. Brooke, he 
only says that he had never seen some pots of structure 
better with his ~.th; this is a clear admission that he had 
seen with the 2,th points of structure not to be seen with 
the ~th; and at the last meeting of our Society, in answer 
