^02 Scienlific Intelligence. 
those with the nearest fixed star. The utmost limits of human 
vision seem attained when such objects are lost to the sight ; and 
this we are led to suppose must take place about the 35000th 
order of distances. 
9. Ashestus Fibres recommended for Micrometers. — Professor 
Wallace, of the Royal Military College, has very ingeniously 
suggested the application of the capillary crystals of asbestus to 
the purposes of micrometrical fibres. Upon mentioning this to 
that celebrated artist Mr Troughton, and putting into his hands 
a small quantity of amianthus, of a pearly whiteness, Mr Trough- 
ton applied a filament, about go’uo diameter, to 
the eye-piece of a telescope. The line was beautifully even, 
and considerably opaque. As the crystals seem divisible beyond 
the limit of the senses of seeing and feeling, it is easy to obtain 
fibres of any degree of tenuity. 
10. Experiment shewing that gravity acts equally upon light 
and heavy bodies . — M. Benedict Prevost has devised the following 
simple experiment for shewing that the retardation in the fall of 
light bodies is owing solely to the resistance of the air. Place a 
piece of thin paper on the bottom of a small box, of such a 
weight, that in falling the bottom will ahvays keep lowermost, 
and having let fall the box and the paper from the height of 
two or three yards above a cushion, they will both reach it at 
the same time ; while a piece of paper of the same size let fall at 
the same time, will flutter slowly and obliquely to the ground. 
The experiment will succeed if the paper is placed on a crown 
or half-crowm piece, without using a box. 
OPTICS. 
Yi, . Singular Optical Illusion seen in BqffiiCs Bay. — Among 
the remarkable illusions which arise from local variations in the den- 
sity, and consequently in the refractive power of the atmosphere, 
we are not acquainted with any more interesting than one which 
was more than once observed by the officers on the expedition 
to Baffin’s Bay. Upon looking at the summits of distant moun- 
tains, they were surprised to observe a huge opening in them., as 
if they had been perforated, or an arch thrown from one to ano- 
ther. This efiect arose from the apparent junction of the tops 
of the mountains, produced by a variation of density in some 
part of the atmosphere between the observer and the tops of 
