266 Progress in Science. (April, 
grind, hard substances, such as granite, metal, or glass, and its action depends 
upon the expulsion, at a considerable velocity, of quartz sand, by a steam or 
air jet passing through a tube, and strikingithe material operated upon. In some 
early experiments made with this apparatus, a hole, 1} inches in diameter and 
13 inches deep, was drilled through a block of corundum in 25 minutes, with a 
pressure of steam of 300 lbs. With roo lbs. pressure a hole, 1 inch by 
4. inch, and 4 inch thick, was cut through a hard steel file in ro minutes. 
At the fair of the American Institute, at New York, last year, a diamond was 
sensibly reduced in weight in one minute, and a topaz was entirely destroyed. 
It is a curious feature of this invention that, whilst hard substances are thus 
rapidly affected, soft and delicate materials are left untouched when exposed 
to the same influence. Thus, if a thin stencil sheet of india-rubber be laid 
over a block of granite or marble, and the blast turned upon it, the stone is cut 
or drilled, while the rubber remains untouched. If a photographic film of bi- 
chromatised gelatine be placed on a sheet of glass, and the jet applied, a pic- 
ture may be engraved, and in the same manner flowers and fern-leaves may be 
reproduced with the utmost delicacy. For grinding glass a very slight pressure 
is sufficient, that produced by air under 4 inches of water being ample for the 
purpose. 
ENGINEERING SOCIETIES. 
Institution of Civil Engineers.—At the fifty-fourth Annual General Meeting 
of this Institution it was announced that there were on the books, on the 30th 
of November last, 14 honorary members, 724 members, 1048 associates, and 
203 students,—together 1989, as against 945 ten years ago. At the first 
meeting in January, Mr. Hawksley, who was elected President at the Annual 
Meeting, took his seat, and delivered an excellent Address, the leading topics 
dwelt on being—the use of the Engineering profession to Government in times 
of war, railway construction, and hydraulic engineering. On the 23rd of 
January a paper was read on ‘“‘ The Somerset Dock at Malta,” by Mr. Charles 
Andrews. This dock is situated in the French Creek. The works were com- 
menced in 1865, from designs by Col. Clarke, and under the superintendence 
of Mr. Andrews. The length on the floor is 428 feet; the length over all, 
468 feet; the width of the floor, 42 feet 6 inches; the width between the 
copings, 104 feet ; and the width of the entrance, 83 feet. The depth of the 
invert, floor, and entrance, below the average sea level, is 33 feet 6 inches. 
The cost of the Dock, inclusive of the caisson, has been about £120,000. 
The entrance cost £ 30,000, exclusive of clearing the rock from the site. 
An important paper, ‘On the Value of Water, and its Storage and Distri- 
bution in Southern India,” was read by Mr. George Gordon, on the 30th of 
January last. From this paper we learn that there are two general systems 
employed in India, namely, Tank and Channel Irrigation. The existing. tank 
irrigation is chiefly of native origin, and may be divided into three classes :— 
1. Tanks formed by the closing of the passage of a considerable river through 
a narrow gorge, in a range of hills, by means of a high dam or ‘ bund.” 
2. Those formed in the plains by embankments carried across the drainage of 
the country, and impounding the water of one or more streams, these tanks 
being of great superficial area, but shallow. 3. Tanks which might be consi- 
dered intermediate between the other two, having in general a greater length 
of dam than the first and a greater depth of water than the second. Few 
examples of the first kind remain entire. Under the head of Channel Irriga- 
tion, it was stated that only rivers of the larger class, which had a continuous 
flow for several months, were available for extensive irrigation projects. The 
smaller rivers were merely torrents, which quickly carried off heavy falis of 
rain and then became dry again. The water, however, is in many cases inter- 
cepted by chains of tanks, of the second or third class, built across these 
torrents. The details of irrigation channels were then dwelt upon, and other 
particulars,—such as their cost of construction, the net profit per acre upon 
various crops, loss by evaporation, &c., which it would occupy too much space 
to follow out in further detail now. 
