1880. | Microscopy. 309 
During this part of their journey they discovered a vast extent of 
fertile country, abounding in grass, and intersected by numerous 
large rivers, all running north and north-west. Great numbers of 
natives. were seen, and “for the most part ine were fine, big men, 
but they had evidently never seen Europeans before. Leaving 
the Victoria, they came to an almost waterless country, and after 
terrible sufferings finally reached the epee telegraph station. 
They arrived at Port Darwin on October 6, 1879.1 
MICROSCOPY.’ 
AGENCY FOR EXCHANGING Osjects.—A Microscope Sra 
Bureau has been opened by Herman Poole, . Sw 
street, Buffalo, N. Y. Slides are to be sent to the exchange in 
quantities of not less than six, and accompanied with a list of de- 
siderata. One of each six will be retained by the agency, and 
the rest will be exchanged as requested, so far as may be possible. 
EXCHANGES OF APPARATUS.—Several subscribers desire to make 
exchanges of apparatus. A Crouch student’s monocular stand, 
and Schrauer binocular, and several choice lenses are offered, 
either for a Beck or Crouch binocular, or a Powell & Lealand 
large monocular, or for lenses of other powers, or for cash. Par- 
ticulars can be obtained from the editor of the Department of Mi- 
croscopy of the NATURALIST. 
AMERICAN Society oF Microscopists.—The executive commit- 
tee of this Society have decided to accept the invitation received 
from Detroit, and the meeting next August will therefore be held 
in that city. The precise date is not determined at the time of 
this writing. It is certain that the citizens of Detroit will give a 
generous welcome to the Society; and a large and important 
meeting is expected. Correspondence in regard to papers to be 
offered, or other scientific business of the meeting, should be ad- 
dressed to the president-elect, Prof. H. L. Smith, of Geneva, N. Y. 
OBSERVATIONS ON THE CONSTRUCTION OF THE -HUYGHENIAN 
EYE-PIECE AS USED IN Microscopes.—The difference in the con- 
ditions under which the Huygenian eye-piece is used in the micro- 
scope, as compared with the telescope, for which it was first de- 
vised, and the adaptation of the eye-piece to those conditions, 
has received but little attention from microscopists, and there are 
discrepancies in the few statements published in regard to 
subject. The following examination of some of the oculars sa 
in use on microscopes was undertaken to determine whether their 
construction conformed to any general principles. The examina- 
tion was made by means of a heliostat and focometer, by which 
the dismounted lenses could be arranged in any position with 
reference to each other. The lenses being arranged in in the foco- 
1 For fuller details of this expedition see Zeitschrift der Gesellschaft für Erdkunde 
zu t Berlin, 1 1879, p. 436. a 
? This department is edited by Dr. R. i wae, T N. Y. ; : 
