1872.] Mechanics. 267 
Institution of Mechanical Engineers —The Members of this Institution met 
at Birmingham on the 25th of January last. Amongst the papers then read 
were two to which we shall here refer, viz., ‘On the Strength and Proportions 
of Rivetted Joints,” by Mr. Walker Brown, of Bristol, and ‘‘ A Description of 
the Disintegrating Flour Mill, and Machine for Pulverising Minerals, &c., 
without Grinding, Crushing, or Stamping,” by Mr. Thomas Carr, of Bristol. 
In the former paper, four different modes of fracture possible in rivetted joints 
were described, consisting in—shearing of the rivet; crippling of the plate, or 
elongation of the rivet hole in the line of strain; fra@ture of the metal between 
the rivet hole and the edge of the plate in the line of strain; ortearing of the 
plate along the line of the rivet holes, at right angles to the line of strain. 
From the consideration that a perfe& joint would be one offering equal resist- 
ance to each of these modes of fracture, the proper proportions were deduced 
for the various descriptions of rivetted joints, with the aid of data furnished 
by different experiments previously recorded, and by a series of experiments 
recently made for the purpose by the writer. 
In the process of disintegration by Carr’s Disintegrator, the particles of the 
material operated upon are shattered in mid-air by a succession of blows deli- 
vered with extreme rapidity in opposite directions, and are thus pulverised by 
the force of the blows alone, without being subjected to the compression or 
friction which accompanies the ordinary processes of grinding, crushing, or 
stamping the material between two surfaces. The disintegrator consists of a 
pair of circular discs, rotating in contrary direCtions upon two shafts situated 
in the same line; the opposing faces of the discs are studded with a series of 
short projecting bars, or beaters, arranged in successive concentric rings or 
cages; and the rings of beaters fixed in one disc intervene alternately between 
those fixed in the other disc, and revolve in the opposite direction. The ma- 
terial to be pulverised is supplied through an opening in the centre of one of 
the discs, and receives from the innermost rings of beaters a centrifugal 
motion, propelling it towards the circumference of the discs: in its course 
through the machine it encounters successively the several rings of beaters 
revolving alternately in opposite directions at a high speed, and the particles 
are thus dashed violently by each beater against the beaters in the next outer 
ting running in the contrary direction, whereby the material is effectually 
broken up and reduced to powder. 
MECHANICS. 
At the Meeting of the Royal Scottish Society of Arts on the 11th of March, 
an apparatus was exhibited by Dr. R. M. Ferguson, for showing the motion of 
waves on the surface of a liquid, and for illustrating more particularly the pro- 
pagation, reflection, and interference of the waves of sound. It is similar in 
principle to that exhibited by Professor Morton, in Philadelphia, and described 
in our last October number. It has the advantage, however, of greater sim- 
plicity, and is merely a combination on an ordinary chemical stand of things 
generally in the hands of a teacher of science, and used for the most part for 
other purposes. The accompanying cut shows the arrangement. / is the 
illuminating lens of a magic lantern. misa plate-glass mirror placed at 45° to 
turn the horizontal light into a vertical direction; ss is a glass saucer made by 
cutting the end from an ordinary glass shade; / a photographic lens; mz a 
second mirror to turn the light again horizontal but at right angles to its first 
horizontal. direction upon a screen. The glass dish is partially filled with 
methylated spirits, and the dropping apparatus, d, intended to excite the waves, 
is filled with the same liquid. This last consists of a Wolff’s bottle funnel, 
furnished with a glass stopcock (of the ordinary German make), bent into the 
form shown, and having its lower extremity where the drop issues drawn out 
into a pipette point. The whole can be fitted to a retort stand with the aid of 
the usual rings and clamps that form the complement of its “‘ fixings.”” The 
great difficulty in making a successful arrangement for exhibiting what must 
necessarily lie horizontal on a vertical screen, is the full illumination of the 
object to be exhibited. The diverging cone of rays that falls on the surface of 
