484 JOURNAL OF SCIENCE. 
(6.) Mr. Trebeck exhibited a curious sample of brown wool, 
having several bands of lighter colour, and he introduced the ques- 
tion as to the felting properties of wool. Messrs. Hirst and Pedley, 
having recently investigated the matter, expressed themselves as 
unable to dissent from the generally received theory that this im- 
portant quality of wool is due to the rough and serrated notches 
always present on a felting fibre Mr. Whitelegge, a visitor, hav- 
ing had practical experience in wool-sorting, and the preparation 
of telt for hat-making, stated that manufacturers generally cleanse 
wool from burrs and seeds by steeping in dilute sulphuric acid, 
whereby the woody matter is destroyed, and at the same time its 
felting properties are impaired, although he was unable todetect any 
alteration in the shape of the “notches.” However, in furs trom 
skins that had been tanned he found the felting properties to be in- 
tensified. Asa proof that felting depends on the presence and 
character of the ‘“‘ notches,” heinstanced the custom of the felt hat 
manufacturer to select and keep separate the little patch of red fur 
always present in the neck of a rabbit skin, known in the trade as 
the ‘‘ red patch,” for the purpose of mixing with other fur and rub- 
bing in over bare patches ina felt, so that what would otherwise 
be a defect, and render the goods unsaleable, is rendered scarcely 
discernible even to a practised eye. He found these “red patch ” 
hairs to be notched to an extraordinary extent. 
Sydney, June 11th, 1883.—Mr. Hirst in the chair. 
A short paper was read by the chairman explanatory of the 
principles upon which the latest objectives of the highest magnifying 
power are now being constructed, entitled ‘‘ What is meant by the 
expression Angular and Numerical Aperture?” Reference was 
more particularly made to the extension of aperture of ‘“‘ homo- 
geneous” lenses over the maximum angle, viz., 180°—capable of 
being given to ‘‘ dry ” objectives—this extension of aperture being 
termed ‘Plus 180: air angle.” ‘‘ Numerical Aperture” was then ex- 
plained as the name given to the standard scale to which objectives 
of every cliss are now reduced for comparison. Dr. Wright ex- 
hibited, on behalf of Mr. Thomas Francis, C.E., a series of photo- 
graphic views of microscopic objects, greatly enlarged, and of ex- 
ceptional excellence. These admirable photographs were taken in © 
one to one and a-half second of time, using direct sunlight, with 
immersion objectives and illuminators. An instantaneous picture 
of a greyhound leaping over a stick was taken with an exposure of 
1-1500 part of asecond. Dr. Ralph, president of the Microscopical 
Society of Victoria, called attention to what he regarded as a 
bacteyrium, found in the living cells of the water plant Vallisnenia, a 
giant specimen of which grows most luxuriantly in the ponds of 
the Botanic Gardens. He has been studying these organisms for 
some months past, and surmises that bacteria are not the actual 
germs of disease, but act as disease carriers. Messrs. Hirst, Ped- 
ley, and Kyngdon exhibited living specimens of Vorticella, Pluma- 
tella vepens, and several other fresh-water organisms. Attention was 
called to the illustration of Floscularia ambigua that appears in the 
last number of the Jourual of the Royal Microscopical Society of 
London. This new variety has been also discovered in the Water- 
loo marshes, and a living specimen was exhibited at the last 
meeting. In the report of the last meeting the specimen of 
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