Fume 1 I, 1885| 
NATURE 
rai 
With regard to the more southerly parts of Eastern Africa, 
and more especially the region between the Mozambique coast 
and Lake Nyassa, our knowledge has lately increased by leaps 
and bounds. The increase has been principally due to the sys- 
tematic explorations of Mr. Consul O'Neill. The general remark 
may be permitted that, thanks chiefly to Mr. O'Neill, we now 
have for the first time a fairly satisfactory knowledge of a region 
varied in its physical configuration, well watered, and fertile, 
which has hitherto remained a blank on our maps, notwith- 
standing the occupation of the coast by the Portuguese for nearly 
four centuries. 
M. Giraud has returned this spring from his exploration of 
Lake Bangweolo and its outlet, and his unsuccessful attempt to 
cross Africa by way of the Upper-Congo ; Mr. Arnot has crossed 
from Natal to the Bihé plateau by way of the Upper Zambesi ; 
Mr. Montagu Kerr has crossed Matabele-land and the Zambesi, 
and penetrated by a new route to the south-western shore of 
Lake Nyassa; and Mr. Richards has reached from Inhambane 
the southern districts of Umzila’s kingdom. In Western Africa 
further additons have been made to our knowledge of the Congo, 
chiefly by the publication of Mr. Stanley’s long-expecied book 
and the maps which accompany it, and by Messrs. Grenfell and 
Comber’s careful survey of the middle course of the Congo and 
the Bochini tributary to the junction of the great river Kwango. 
The members of the French Expedition on the Ogowé and the 
northern tributaries of the Congo have also been doing good 
work in the survey of the territories newly acquired by France. 
In South America a striking feat of exploration has been ac- 
complished since my last address; the supposed inaccessible 
summit of Mount Roraima, on the confines of British Guiana and 
Brazil, was reached in December last by Mr. im Thurn and his 
companion, Mr. Perkins, accompanied by a small party of 
Indians. 
In conclusion Lord Aberdare gave the following brief sum- 
mary of the Admiralty surveys of the year 1884, for which he 
was indebted to the hydrographer, Capt. Wharton, R.N.: The 
continuous prosecutions of marine surveys in different quarters 
of the globe has been well maintained during the past year. The 
two home-surveying vessels have been employed, one on the 
west and the other on the east coast of Great Britain. On 
foreign surveys 60 officers and 500 men haye been employed in 
four steam ships of war and five other smaller vessels. These 
ships have been at work in Newfoundland, the Bahama 
Islands, Magellan Straits, South Africa, Red Sea, Malay 
Peninsula, coasts of China and Korea, north-west coast 
of Australia, and amongst the Pacific islands. The most 
important additions to our hydrographical knowledge are 
as follows:—The survey of the Little Bahama Bank will be 
shortly finished, and the same may be said of the southern shore 
of Newfoundland. The survey of the main sirait of Magellan, 
to which reference was made in the last address, was completed 
early in the year. Many useful additions have been made to 
ports and salient parts of the coast of south-east Africa. In 
the Red Sea the intricate approaches to Sawakin have been well 
laid down. On the west coast of the Malay Peninsula, Penang 
harbour has been re-surveyed and the positions of the islands 
lying to the north-west and forming the eastern boundary of the 
ordinary route of vessels to Malacca Strait have been accurately 
determined. The unknown western shores of Korea, south of 
the approach to Seoul, for two degrees of latitude have been 
explored, and the main features of this island-studded shore 
laid down. New rivers and harbours have been entered, 
notably, the large river Yeun-san-gang, at the entrance to 
which stands the considerable town of Mokfo. There appears, 
however, to be little chance of immediate trade with Korea, in 
consequence of the absence of any valuable products and the 
scanty needs of the population. The southern approach to 
Haitan Strait on the Chinese coast, much used by British trade, 
has been re-charted. On the difficult shores of Western Australia 
such progress has been made as the small means at the disposal 
of the surveyors has permitted. In the Solomon Islands the 
Bougainville Strait has been charted. This Channel will in the 
future be most probably a highway for traffic between Eastern 
Australia and Japan. Many additions have been also made to 
the charts of various groups of other Pacific islands. The survey 
of the coasts of India carried on by officers of the Royal Navy 
and India Marine has been actively progressing. Surveys of 
Rangoon, Cheduba, and other ports in the Bay of Bengal, as 
well as harbours on the west coast of Hindostan, have been 
made. A re-suryey of the great Canadian lakes has been com- 
menced in Georgian Bay, where trade by water is on the 
increase. 
Lord Aberdare then intimated his resignation of the Presidency 
of the Society, the Marquis of Lorne having been elected to 
succeed him. 
PROF. REYNOLDS ON THE STEAM 
INDICATOR* 
‘THE object of this paper was to define the causes and extent of 
the disturbances in indicator diagrams. The theory, as 
given, had been taught for several years in Owens College; but the 
publication had been deferred to enable an extensive series of ex- 
periments to be made. These experiments had now been carried 
out by Mr. A. W. Brightmore, Stud. Inst. C.E., late Berkeley 
Fellow in Owens College. In the first place it was shown that 
there were five principal causes of disturbance, namely: the 
inertia of the piston of the indicator and its attached weights ; 
the friction of the pencil on the paper, and its attached 
mechanism ; varying action of the spring ; inertia of the drum ; 
friction of the drum. 
The effect of the inertia of the pencil and its attached mechan 
ism presented 2 mathematical problem, by the solution of which 
it was shown that there were two disturbances from this cause : 
one, a general enlargement of the mean indicated pressure, de- 
pending on the weight of the moving parts of the indicator, the 
stiffness of the spring, and the square of the speed. The other 
disturbance was a vibration of the pencil. _ Every indicator piston 
vibrated when disturbed, so that the period of vibration depended 
on the stiffness of the spring. 
The error which these oscillations caused in the area of the 
diagram depended on their magnitude, and, to a greater extent, 
on the smailness of the number in a revolution. But the evil of 
these oscillations was not so much an effect on the area as in the 
disfigurement and the confusion they produced in the diagram. 
So long as there were thirty of these oscillations in a cycle. the 
necessary fluid friction of the indicator piston would so far reduce 
them as to render a fair diagram possible, but when the number 
was as low as ten it was all the pencil could do to prevent them 
upsetting the diagram. 
The friction arising from the pressure of the pencil always 
acted to oppose the motion of the pencil, and therefore rendered 
it too large during expansion and exhaust and too small during 
compression and admission, and thus the general effect was to 
increase the size of the diagram. This friction consisted of that 
of the pencil on the paper ; and that of the mechanism, caused 
by sustaining the pressure of the pencil. The effect of the 
friction of the pencil was greatly reduced by the motion of the 
paper. The magnitude of these effects taken together on the 
area of the diagram depended on the construction of the instru- 
ment and on pencil-pressure. From numerous experiments It 
would appear possible to make a difference of as much as five 
per cent, in a locomotive in mid-gear by pencil-friction. _ 
The couclusions, as regarded the motion of the pencil, were 
that the general effect of inertia and friction were both to increase 
the size of the diagram; that so long as the speeds were such 
that the number of vibrations of the pencil during a revolution of 
the engine was not greater than fifteen, the effect of inertia was less 
than one per cent., but that, if the number was greater than thirty, 
oscillations would show themselves unless the pencil-friction was 
increased. They might, by this, be kept down till the number 
of vibrations was equal to fifteen, but not farther, and then the 
necessary friction would affect the area of the diagram about five 
per cent. For the diagrams to be sensibly accurate, and free 
from oscillation, the speeds must not be greater than would make 
the number of vibrations equal to thirty. These speeds were 
given in the paper for Richards’ indicators. 
The effect of the inertia of the drum with an elastic cord was 
shown to be a nearly uniform elongation of the diagram. The 
result of the varying stiffness of the drum spring was a nearly 
uniform contraction. With Richards’ indicator these two latter 
disturbances neutralized each other at a speed of 150 revolutions 
per minute. Ai other speeds the effects were apparent in the 
length of the diagram ; but, except when the expansion was great 
and the connecting rod short, they did not affect the indicated 
pressure. The friction of the drum with an elastic cord caused 
the cord to be longer during the forward stroke than during the 
¥ A Paper read at the Institution of Civil Engineers, May 19, **On the 
Theory of the Indicator and the Errors in Indicator Diagrams,” by Prof. 
Osborne Reynolds F.R.S. 
