146 
POPULAR SCIENCE REVIEW. 
Thus satisfactorily are some of the minute wonders of creation, 
the objects we can neither see nor touch, interpreted by the 
equilateral prism. In its extended application it has made the 
microscope, old observer as I am, quite a new instrument to me, 
and my friend, Mr. Sheppard of Canterbury, felt constrained to 
say, after witnessing prism work, that As the microscope makes 
a new start on the Queen’s birthday 1869.” 
THE PODURA. 
Another object, which Burns 'would class among our “ bonnie 
wee things,” is the scale of the Podura, now offered to us under 
the more sonorous title of Lepidocyrtus curvicollis. In the 
postscript to my paper on idle Equilateral Prism I offered a 
contribution on its structure, and attempted to remove some 
prevailing misapprehensions. This minute scale, a very favourite 
test with practical opticians, appears under prism illumination 
to consist of two membranes, between which there is a series 
of small solid spherules or beads. Under a power of 12,000 
linear, I find 24 beads in toVo^k °f an i n °h on 12 -inch 
horizontal diameter of the field, and 6 on the vertical. Hence, 
in the latter direction they are about 6 0 T 0 0 th of an inch apart, 
and in the former, the interval being equal to a diameter of a 
spherule, they are about 4 8 - ^ o, 0 th of an inch apart This is the 
utmost I have been able to accomplish. That I have not done 
more is an indication either of want of skill in the observer, or 
of want of penetration in the magnifying power, and fortunately 
recent examination has proved that neither the observer nor his 
illuminating apparatus is in fault. The defect is in the power. 
DR. ROYSTON PIGOTT’S RESEARCHES. 
When my own -^th, a choice power, carefully selected for 
me by Mr. Boss, or an almost perfect £th by Wray, is removed 
from my own microscope to Dr. Pigott’s, it is brought under 
the influence of his “ Aplanatic Searcher,” a system of lenses, 
between the eye-piece and the power, which detects and 
remedies residuary spherical aberrations, and I can now see 
with my own powers what had been heretofore invisible, viz. 
the beautifully beaded structure of the whole test scale as dis- 
covered and -described by Dr. Pigott. Mr. Slack, himself an 
eye-witness, thus announces the interesting discovery: — 
“ Dr. G. W. Royston Pigott has recently astonished the 
world of microscopical observers, by telling them very plainly 
tw’o startling, and to many unwelcome, truths , for such we must 
pronounce them. First, he says that they have not seen their 
favourite test object, the Podura scale (Lepidoci/rtuscurvicollis), 
