488 
accordingly we find three of the largest objectives 
in the world, — the 27-inch at Vienna, by Grubb; the 
23-inch at Princeton, and the great Russian 30-inch, 
both by Alvan Clark & Sons, with their lenses sep- 
arated by a considérable interval. 
Assuming a large lens to be made of satisfactorily 
good disks, and having its curves and interval so ad- 
justed as to give the best attainable results, there is 
another detail of construction which demands in- 
creased attention with every augmentation of size; i.e., 
the state of the surfaces of the lenses. Formerly it was 
too readily assumed, that, provided the curves were 
right, a few scratches more or less did not matter. 
There is a well-known story of an optician, who, on 
being blamed for turning out a badly scratched lens, 
replied that an object-glass was to be looked through, 
and not at. The optician was nevertheless in the 
wrong; for if delicate objects are under examination, 
no matter whether they are small companions of large 
stars, or minute satellites of bright planets, there can 
be no doubt that the finish of the objective plays a 
considerable part in their visibility. Nor is it merely 
necessary that the surfaces should be correctly formed 
and well polished: it is also requisite that they should 
be kept scrupulously clean, and, above all, free from 
grease, the slightest trace of which, when spread over 
a lens, must throw out irregular diffraction spectra, 
materially affecting the visibility of any small point 
of light in the neighborhood of a brilliant object. 
In this respect no practical astronomer should neglect 
to assure himself that an object-glass is really doing 
full justice to the maker. 
Dr. Copeland’s remarks on the mountings of large 
equatorials are especially pertinent. In America, he 
says, the mounting is just or barely sufficient to per- 
mit of a satisfactory use of the grand optical powers 
of their larger instruments; and no refined detail of 
auxiliary apparatus is attempted. On the continent 
we find the convenience of the astronomer studied in 
the most painstaking manner, and perhaps in no 
instruments in the world is this so carefully kept in 
view as in the finer German instruments. This is 
doubtless due in no small measure to the intimate 
relations which exist between the chief continental 
instrument-makers and practical astronomers; so that 
just that kind of apparatus is provided which expe- 
rience has shown to be requisite. On the other hand, 
in the stability and rigidity of their mountings, the 
larger English and Irish instruments stand preemi- 
nent, while they year by year show a greater variety 
of really available subsidiary apparatus. Indeed, 
there can be little room for doubt that the elder 
Grubb, by his elegant arrangements for relieving the 
friction of both axes of the equatorial mounting, 
practically removed all limits to its size and strength; 
while in the little-known 25-inch refractor at Gates- 
head, by Cooke & Sons, we have a telescope which 
only requires to be efficiently used in a good atmos- 
phere to show its great merits in all respects. 
Finally, Dr. Copeland thinks, that whether we 
take large European or American instruments, the 
prospect is most encouraging, both to the astronomer 
and the instrument-maker. Nowhere can signs be 
SCIENCE. 
PP ore a or 
[Vou. III, No. 63 
detected that the utmost practical limit has been 
reached. A 27-inch glass can be managed with prob- 
ably greater facility now than a 10-inch fifty years 
ago, and with something closely approaching to the 
full gain in power, due to increased size. The ques- 
tion of size now, as it did then, reduces itself to the 
production of suitable disks of glass and to cost. 
Here it is that silvered-glass reflectors offer facilities 
of which several distinguished investigators have not 
been slow to avail themselves. 
ENTOMOGRAPHY OF HIRMONEURA. 
Dr. FRIEDRICH BRAUER has, during the past sea- 
son, been able to add considerably to our knowledge 
of the life-history of the Hirmoneura obscura, and 
the results of his observations have been published 
(Sitzungsb. akad. wiss. Wien, p. 865). During the 
latter part of June he found within the nearly formed 
pupa of Rhizotrogus the second larval stage of the 
Hirmoneura, which resembles the first stage in the 
structure of the mouth-parts (see Science, No. 12), but 
lacks the pseudopods and ambulatorial filaments so 
characteristic of that stage. How and when the young 
Hirmoneura larva gets at the Rhizotrogus larva still 
remains unknown; but Brauer assumes (and I think 
he is quite safe in doing so) that it enters the larva 
(not the pupa) of the Rhizotrogus, and is a true para- 
site, and not merely a predaceous insect. Having 
entered the Rhizotrogus larva, it seems highly proba- 
ble that the Hirmoneura larva has to undergo a kind 
of quiescent larval state of uncertain duration, but 
which suddenly changes to one of rapid development 
during the pupal state of the beetle, which lasts only 
from two to three weeks. Hirmoneura larvae in the 
second stage, of about eleven millimetres in length, 
were found in Rhizotrogus pupae; and ten days after- 
ward the full-grown parasitic larva, twenty-two milli- 
metres in length, was found. Brauer thinks it more 
than probable that the full-grown Hirmoneura larva, 
after emerging from the Rhizotrogus pupa, hibernates; 
the perfect fly appearing in July of. the next year. 
This seems to me more doubtful. The Rhizotrogus 
larva is known to require two years for development. 
There are two alternatives for the Hirmoneura larva: 
either it is carried, by clinging to the beetle, into the 
ground, and remains quiescent, either attached to or 
near the Rhizotrogus larva, for nearly two years; or it 
is capable of independently discovering the Rhizotro- 
gus larva when this last is in its second year’s growth. 
The first seems to me the most probable, and would 
give two years for the development of the Hirmoneu- 
ra, or even three if the full-grown larva hibernates, In 
either case, the young Hirmoneura larva is endowed 
with a sense which is truly marvellous, whether we 
choose to attribute to it consciousness of its acts, or 
ascribe them to ‘blind instinct.’ 
Brauer raises a curious practical question, which 
would indicate that old pine fences or felled trees in a 
field may, in this particular case, serve to prevent 
the undue multiplication of the Rhizotrogus ‘ white 
grub.’ C. V. RILEY. © 
