256 On the Advaneing Aplanatic Power [Monthly Microscopteat 
structure of both sets of these strie. I can see them to the greatest 
advantage with a power of 800 and a fine half-inch objective; great 
penetration is required rather than large angular aperture. 
I have never yet carefully examined striated scales without 
developing beaded structure such as— 
The Morpho Menelaus: Finest scales of Azure blue. 
Pieris Olearacea. 
Popurmz: Macratoma maritimus. 
Templetonia witida. 
Podura Transit.* Macratoma plumbea, in confirmation of this 
law. 
It is somewhat surprising to me that animadversions have 
almost entirely been confined to one illustration in the “unwelcome” 
paper; the particulars marked A, B, C, page 302, XII., exciting no 
examination. But they may be strongly recommended to the 
attention of microscopists. 
But so soon as it shall be ascertained that false appearances 
supported by “ authority ” are accepted as the true; that unknown 
objects are reasoned upon as if they were known ; that the creations 
of the combined errors of the observing instruments, transfigured 
according to the taste of the partisan, are accepted as perfect tran- 
scripts of nature; that, in fact, the unknown is interpreted by a 
phantasm, a mockery of nature’s truth, the philosophy of the micro- 
scope will be doubtless degenerating into a dogmatic and ignoble 
science, falsely so called. 
Natural test-objects have in many cases proved delusive in a 
high degree. 
Whenever such objects consist of several complex transparent 
or rather translucent structures arranged in different planes closely 
contiguous, false images commingle themselves with the true belong- 
ing to a given focal plane, and the resultant image is, under the 
highest magnifying power, more or less a MIRAGE. 
In order to obtain the true image belonging to a given focal 
plane, the false images must be put as much as possible out of the 
way—removed or displaced ; a desideratum hitherto unknown. 
I hope on another occasion to be able to direct the attention of 
microscopists to some observations in this new field of research. 
But to proceed with the subject-matter of this paper, we cannot 
contradict the fact that the advancing powers of the microscope 
have been but slowly developed by faltering steps. 
It was first discovered that “lined objects” could only be de- 
veloped by increasing aperture. Scales and diatoms were now con- 
stantly examined for their markings and structure. As the objects 
increased in difficulty, contrivances, ever new, were invented to over- 
* Found by Mr, Reade on his transit instrument. 
