SUMMARY OF RESULTS. 
5 7 
of his Geodesy to the study of the question : “ Wie die Tieffc einers Weihers, Graben, 
See und anderer stillstehender Wasser, sollen kiinstlich abgemessen und ergriindet 
werden?” He takes a hollow tin ov copper sphere, hermetically closed, and provided with 
an eye by which a metal plate is attached. The top of the plate is furnished 
with a hook fitting into the eye of the sphere, the under part being fitted with 
a heavy foot. Whenever the apparatus touches the bottom the sphere is freed from the 
hook, and returns to the surface. This is exactly the idea of Cusanus, but Puehler 
added an apparatus to act as a clepsydra, measuring the time the sphere takes to 
re-appear. For this purpose he advises the use of a clay vase with a small hole at the 
bottom. The moment the bathometer is dropped, the vase is applied to the surface of 
the water, which filters through the small orifice at the bottom. He had noted the 
quantity of water entering the vase in a former experiment with his bathometer in water 
of which he knew the depth. 
Cusanus’ idea was again taken up by a Neapolitan architect named Alberti, of whom Alberti’s 
Blancanus 1 speaks in a work on architecture. Alberti describes an apparatus con- Apparatus ' 
sisting of a heavy sphere (a) and a light bent metal tube (6), which is released on 
touching the bottom, and acts as a float. He says : — “ Given water of known depth (p), 
b requires t (time measured by the clepsydra) to return to the surface, then you have 
for an unknown depth t 1 :t=p 1 : p, p = 
h 
Cusanus, Puehler, Alberti, and all their successors who have endeavoured to solve the 
problem of the depth of the sea by means of apparatus with self-detaching floats, take it for 
granted that the descent of a heavy body through a resisting medium, such as water, is 
always uniform. This is only approximately the case. One might, indeed, admit that, 
when the appliance goes down, the velocity is very nearly uniform, for resistance here 
paralyses acceleration ; but we must also admit that there will be acceleration of motion 
when the float, detached from the weight, returns to the surface. 
More than a century later Robert Hooke continued these bathymetrical experiments. Hooke’s 
He had a sphere made of wood, well varnished, and provided with a steel spring, to which AFl arat 
a piece of metal was suspended ; this became detached on coming in contact with the 
bottom, and allowed the float to ascend. 2 Soon after this Rochon made experiments 
in the Indian Ocean with a modified apparatus of this celebrated English physicist. But 
sinken : und wenn du das erden gefass auf daz wasser setzest und das wasser beriirt, lasse die Kugel auss der hand : 
damach sihe wenn die Kugel uber daz wasser auffart : in dem selben augenblick verhalt das lbchlein das an dem boden 
des erden gefass ist : als dann weg das wasser das in den erden gefasse gefunden auf das alter fleyssigest, merek das 
gewicht, wie sell war es gewogen hat : dergleichen siiclite oder messe auch die tieffe des wassers, an dein ort da du das 
instrument gesenkt hast : und was fiir eine Proportion der Zal der Schware des gewichts des wassers zu der Zal der 
klaffter und tieffe des wassers hat: solche Proportion wird auch haben die zal oder schware des wassers in det erdi :i 
gefasse gefunden, wie jetz gesagt, zu der zal der Ivlaffter, die die tieffe des wassers ist” (Ein kurtze und grundlichc 
anlaytung zu dem recliten Verstand Geometric, Dillingen 1563, p. 652). 
1 Blancanus, Spluera mundi seu Cosmographia, Mutinae, 1635, pp. 1470 et seq. 
2 See Phil. Trans., vol. ii. pp. 439 et seq., 1667 (reproduced in the tail-piece to this Introduction). 
(summary of results chall. exp. — 1894 .) 
S 
