py sae: Fate ic oe 
30 Prof. Bailey on a new locality of Microscopic Test-objects. 
subjected to experiments by him. That the balsam-mounted 
specimens of all these objects can be satisfactorily resolved is 
well known to American observers, and the following statement 
given by Judge A. 8. Johnson in vol. ‘xiii, p. 32 of this Journal, 
is fully confirmatory of my own experience. Speaking of a new 
object-glass of 1743° niceties in July, 1851, by Spencer, the follow- 
ing remarks are made 
“The light failing t us as evening was: approaching we did not 
try in this way — the pa test or the Providence Gramma- 
tophora, but in the evening we saw both these objects [balsam- 
mounted] satisfactorily scents into dots by unreflected oblique 
light from one wick of a common bed-chamber lamp, burning oil, 
a homely but very effective method of illumination for objectives 
of large apertures.” 
It appears then that the resolution of balsam-mounted speci- 
mens of difficult test-objects can be accomplished, in spite of Mr. 
Wenham’s arguments and experience to the contrary. The error 
in his arguments will be sufficiently obvious to any one who will 
trace the course of a divergent pencil of rays out of the balsam 
instead of into it, as in Mr. Wenham’s experiments, and it will 
then be seen that large angles of aperture are as useful for balsam- 
mounted specimens as for others. I leave the defense of large 
angles of aperture to the professed optician, being well satisfied 
that, notwithstanding the extraordinary attempts made by certain i 
writers in England to underrate the value of the improvements 
made in this direction, no one who has once employed a properly 
corrected object-glass of large aperture will ever be satisfied with 
one of a different construction. 
SESS hcg eer mee semen cegiernenieieines i> rrrcmeannmageen.-— reel Naeger nv aebhievigamatin setgpaplessieesceoln 
On a new locality of Microscopic test-objects. 
a Smithsonian memoir published in February, 1854,* I have 
described and figured a species of Hyalodiscus from Halifax, Nova 
Scotia, which appeared to me to be admirably fitted for a test- 
object, in as much as its circular form with radiant and curved 
lines of great tenuity proceeding in all directions renders it unne- t 
cessary ever to change the position of the shell when in the field 
of view in order to secure the best possible direction of the light. 
Whatever its position, on account of the perfect symmetry of its 
orm and markings, some portion must always be in the best pos- 
sible position with reference to the oblique light used for its ex- 
amination. Unfortunately the Halifax specimens of this beautiful 
object appear to be quite rare, I am therefore happy to announce 4 
nee Peavery upon various Alge from Monterey, California, of: 
an i tbls Sapp y of a species of Hyalodiscus closely allied 33 
cies and answering equally well as a test-object. 
renie nt as a hae ys.cc pace nieg om 
s of the microscope. 
