808 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
menfc. This is absolutely indispensablo owing to the intense heat of 
the source of light (1*43 calories per second). It consists in pouring 
over the whole Microscope and polariscope a fine spray of liquid car- 
bonic acid. So great is the cooling effect produced that an expenditure 
of only 0*00078 grin, per second is required. The linear magnification 
of the instrument is, with ordinary objectives, 11,000, and with oil- 
immersion lenses, as high as 16,000. 
Eustachio Divini’s Compound Microscope.* — Sig. P. A. Saccardo 
describes an ancient Microscope, bearing the inscription “ Eustachio 
Divini in Roma, 1672,” which is preserved in the Museo di Fisica, 
Padua, where, however, nothing further is known as to its history. A 
Microscope of Divini is fully described in the ‘ Giornale dei Letterati ’ 
L (1668).f The present instrument is in many respects similar to the 
one there described. It consists of four tubes of cardboard covered with 
parchment coloured green and gilded. These slide with friction one 
within the other, and each has marked upon it in gold the points of 
different extension (I., II., III., IV.). The largest tube has a diameter 
of 8 cm. When all the tubes are closed up as much as possible, the 
total length from eye-piece to objective is 36*5 cm. When all are 
drawn out as far as the marks I., II., III., and IV., the total length is 
41, 49, 54, and 56*5 cm. respectively. The lowest tube carries on its 
lower half a broad projecting spiral band of cardboard covered with 
parchment, which gears into a corresponding spiral cut into the card- 
board cylinder round which is the brass band bearing the inscription. 
This band is supported by three divergent feet of brass 15 cm. long. 
The objective, consisting of a biconvex lens 8 mm. in diameter and 
2 mm. thick at the centre, is fitted by means of a screw cap into a brass 
tube 5*5 cm. long and 2 5 cm. in external diameter. On a screw- 
thread round this tube moves another tube, in the lower part of which, 
through two side slits, passes the object-holder, which is kept firm by a 
spring. The object is focused by raising or lowering this tube on 
the screw-thread. 
The eye-piece is formed of a large somewhat yellow biconvex lens 
6 cm. in diameter and 5 mm. thick. It is inclosed in two wooden 
rings into which the first tube of the Microscope euters. Thus the 
special eye-piece system of Divini, which consisted of two plano-convex 
lenses, is wanting. In all probability these have been lost, in which 
case the lens just described should be regarded as the field lens. 
Invention of the Compound Microscope.J — Sig. P. A. Saccardo 
publishes several of the documents bearing on the claims of Janssen, 
Galileo, and Drebbel. Criticizing these he comes to the following con- 
clusions: — The testimony of P. Borel in favour of Janssen has no 
documentary value. The documents published by Govi show that the 
first inventor of the compound Microscope (with concave ocular and 
direct vision) was Galileo in 1610. The documents published byRezzi, 
which are in harmony with the testimony of Gassendi and Huygens, 
show that Cornelius Drebbel was the reformer of the Galilean Micro- 
scope, or was in 1620 or 1621 the inventor of the Keplerian compound 
* Atti R. Istit. Veneto Sci., II. vii. (1891) pp. 817-27. 
t See Dallinger’s Carpenter, p. 181. % Malpighia, v. (1891) pp. 40-61. 
