112 REPORT—1862. 
between them, there is suspended a metallic needle insulated from the whole 
of the apparatus, but in communication with a Leyden jar, to which is given 
a constant charge measured by the angle of torsion made by another needle 
suspended to the thread of another apparatus, With the first needle there 
moves a small mirror, on which falls the light of a lamp reflecting upon the 
registering cylinder where the electric curve is produced upon sensitive paper. 
Another fascicle of light which comes from the fixed mirror gives the base- 
line. One of the semicircles being in the state of the earth’s, and the other 
in that of the atmosphere’s electric tension, and the needle which moves at 
the top of the space which separates them having a known and constant 
electricity, it is clear that the slightest alteration in the difference between 
the tensions, or in the quality of the electricity by which they are produced, 
will be directly indicated by the movement of the needle which impresses 
itself immediately on the photographic paper. If this instrument receives at 
Kew the attention of which inventions conducing to the advancement of 
science are there thought worthy, and if any imperfections which may be 
discovered in it in practice are successfully removed, Professor Thomson will 
have the honour of haying discovered the most sensitive and instantaneous 
electrometer in existence, which will doubtless smooth the great difficulties 
which impede the advance of the science of atmospheric electricity. In the 
presence of this electrometer the electric apparatus employed at Greenwich 
will fall into disuse, as it has already done at Kew, where it is dismantled. 
Of the other meteorological instruments in the Kew Observatory, I will only 
mention the great standard barometer, or rather the process by means of 
which its large tube is filled. The barometer and a cathetometer, with 
which are observed the differences of level of the indices of the mercury in 
the cistern and in the column, are fixed to a wall which formerly supported 
the mural gradient of the Astronomical Observatory. It is essentially the 
barometer of Regnault ; but it can turn around its axis, which is adjusted in 
the vertical position by means of screws of pressure: the indices move until 
they touch the surface of the mercury of the cistern; one terminates in an 
edge, the other in a cone: the diameter of the tube is 1*1 inch.” 
Prof. de Souza here describes in considerable detail the process of making 
and filling such a barometer-tube. [For this process the English reader is 
referred to Mr. Welsh’s original paper in the Philosophical Transactions for 
1856, Art. XXTIT.] 
Before returning to London, Prof. de Souza visited the Gardens at Kew, 
and takes occasion to express his very great admiration of the gardens, the 
palm-house, and especially of the museum. He then proceeds as follows :— 
“In London I addressed myself to Major-General Sabine. I haye great 
satisfaction in declaring thus publicly, that the relations acquired with this 
courteous gentleman so long engaged in magnetical science, constitute one of 
the most valuable acquisitions which I made in England. It is known that 
General Sabine has. devoted himself for almost half a century, with an ardour 
and activity never interrupted, to the study of terrestrial magnetism. From 
1818 to 1822 he made four successive long scientific voyages ; in 1837 he 
published the first general map of the isodynamic lines of the globe; after- 
wards he brought about the establishment of four observatories very differ- 
ently circumstanced in regard to the intensity of the terrestrial magnetic 
force, and in opposite positions in regard to the magnetical and geographical 
poles and equators—. e. the observatories of Toronto, Hobarton, Cape of 
Good Hope, and St. Helena. He has also superintended these establishments, 
and reduced and analysed their observations, from whence have resulted 
