23 
of the tanks and form sludge, which is removed, dried, and used as a 
manure. 
Secondly. The breaking down of the potentially offensive and complex 
organic compounds into simple and inoffensive inorganic substances. 
This is accomplished on biological filters. There are many different 
types of filters, but the essential element for success in all of them is that 
atmospheric oxygen must have free access to all parts of the filter. 
A filter may be composed of materials such as clinker, coke, gravel, 
sand, &c. The sewage (usually after settlement in tanks) is passed 
through the filters, and the organic compounds are deposited on the 
surfaces of the filters as a colloidal jelly. This jelly has the property of 
attracting and adsorbing the various compounds in the sewage when the 
sewage is passed over it. 
The jelly itself is also permeated with micro-organisms, macro-organ- 
isms, enzymes, &c., which convert the deposited sewage into inoffensive 
matter. 
The same processes occur in the land of sewage farms. 
Filters are expensive to build, and chemists are endeavouring to find 
a biological method of precipitating the bulk of the sewage organic sub- 
stances which can be removed as sludge in tanks, and thus lessen the 
area of filters required to purify the remainder of the organic substances. 
THE FOURTH DIMENSION. 
By Tue Rey. R. A. Tsomas, M.A. 
The lecturer approached the subject from the mathematical point of 
view. Space, as we know it, possesses length, breadth and height, and 
ean be referred to three axes mutually at right angles. Why not imagine 
a fourth axis at right angles to each of these three? The mathematics of 
such four-dimensional space can be worked out in great completeness. 
Professor Cayley asserted at a British Association meeting that every 
mathematically-obtained conclusion had an _ objective counterpart in 
actuality. Mention was made of “ Flatland—a romance in many dimen- 
sions,’ by Dr. Abbott, as forming an easy introduction to the subject. 
This work of fiction is valuable for its study of the probable difficulties 
of two-dimensional beings (if such exist) in endeavouring to comprehend 
three-dimensional conditions. 
The lecturer illustrated, by a series of models, Mr. C. H. Hinton’s 
method of attempting the realisation of the fourth dimension, assuming 
its spatial existence. Some notes on the history of the subject followed, 
with a consideration of results, practical and philosophical, which would 
arise from the Fourth Dimension. The lecturer pointed out at the close 
that the Fourth Dimension, if it exists, might be, not one of space, as 
represented by the fourth axis, but one supplementary to the three funda- 
mental units of length, mass and time. An interesting discussion followed. 
MICROSCOPICAL SECTION. 
4 Two Meetings of the Section have been held this Session, viz., on 
zs November 24th, when the Chairman, Dr. J. Elliott, exhibited slides of the 
Microscopic Anatomy of Fish, which he had prepared and fully described. 
On February 19th, Mr. A. E. Goodman gave a paper on “ Leaves: 
A Microscopical Study,” making special reference to the transpiration of 
plants. He dealt with the vital functions of plants relegated to leaves— 
respiration, transpiration, assimilation, tissues of a typical leaf and their 
functions, modifications of structure to suit differing environments, 
