SCIENTIFIC SUMMARY. 
443 
near liis compass, wlien tlie needle followed it around the same as it would 
a true loadstone. 
Lord Caithness's Mariners^ Compass. — The compass invented by the Earl 
of Caithness has the following peculiarities : Instead of the two concentric 
brass rings having their axles at right angles, known as gimbals, Lord 
Caithness employs a pendulum and ball, which ball works in a socket in 
the centre of the bottom of the compass bowl. The compass works, there- 
fore, on one bearing on the ball-and-socket principle, and thus maintains its 
parallelism with the horizon in the heaviest weather. 
Browning's Miniature Spectroscope. — This little instrument, which can 
easily be carried in the waistcoat pocket, is yet a most perfect piece of appa- 
ratus \ showing Fraunhofer’s lines well, and bringing out the absorption of 
coloured liquids very distinctly. It contains four prisms and an ingeniously 
contrived adjustable slit. For medical and general 'spectroscopy it will be 
found very valuable. 
The Open Polar Basin (?) — This is a subject hardly physical,” and yet it 
touches very closely a question of astronomical physics. Some very impor- 
tant observations have been recently made upon it by Captain Hamilton, in 
a paper before the Eoyal Geographical Society. The author having ex- 
pressed his belief that Baffin’s Bay consists of an agglomeration of floes of 
ice kept apart by gales and tides, goes on to say that, reasoning from 
analogy, he infers that the Polar basin, which is of much larger extent than 
Baffin’s Bay, must consist of similar floes always in motion where there is 
an outlet, and therefore he doubts the practicability of spring sledge-travel- 
ling from Spitzbergen towards the Pole, and advocates the Smith Sound 
route for sledge operations ; he also believes the best prospect of a ship 
making progress is by keeping close to the weather shore. No arctic 
voyager takes the pack if he can avoid it. His observations lead him to the 
conclusion — 1. That there is no practical proof of a warm under-current 
into the Polar basin, or ameliorated climate caused by its rising to the 
surface. 2. That the migration of birds is no proof of it. 3. The season at 
which the open seas of Penny and Morton were seen only show that local 
causes produce an earlier disruption of the ice there than elsewhere. 
4. That the drifts of the Advance, Fox, and Resolute w^ere quite unconnected 
with any movements of the ice in the Polar basin, and were owing entirely 
to local causes. 
Dr, Miller'' s Thermometer for Deep-sea Soundings. — Several experiments 
having convinced Dr. Miller that the ordinary deep-sea thermometer gave 
too high results, owing to the effect of pressure on the bulb, he was led to 
devise an instrument to be used in Dr. Carpenter’s expedition (the one now, 
we suppose, concluded), which would give accurate results. The expedient 
adopted for protecting the thermometers from the efiects of pressure con- 
sisted simply in enclosing the bulb of a Six's thermometer in a second or 
outer glass tube, which was fused upon the stem of the instrument. This 
outer tube was nearly filled with alcohol, leaving a little space to allow of 
variation in bulk due to expansion. The spirit was heated to displace part 
of the air by means of its vapour, and the outer tube and its contents were 
sealed hermetically. In this way, variations in external pressure are pre- 
vented from affecting the bulb of the thermometer within, whilst changes 
of temperature in the surrounding medium are speedily transmitted through 
