Royal Society. 151 
Sir William Blizard, Knt.; Sir David Barry, Knt.; The Marquis of 
Breadalbane ; The Earl of Charleville ; The Bishop of Cloyne ; The 
Earl of Darnley; Lord De Dunstanville; Colonel Sir Augustus Simon 
Frazer, K.C.B.; Major-General Hardwicke ; Captain Kater; Rev. 
Thomas Robert Maithus, Thomas James Mathias, Esq.; William 
George Maton, M.D.; Rey. Robert Morrison, D.D.; Michael Thomas 
Sadler, Esq.; Richard Sharp, Esq. ; William Smith, Esq. ; Edward 
Troughton, Esq.; Sir George Lemon Tuthill, Knt. M.D.; Ralph 
Watson, Esq. 
On the Foreign List.—Frederich Stromeyer. 
The Secretary stated that of these only three, namely, Captain 
Kater; John Brinkley, Lord Bishop of Cloyne, and Edward Trough- 
ton, Esq. have contributed papers to the Royal Society. 
Capt. Kater contributed the following papers, fifteen in number, to 
the Philosophical Transactions. 
1. On the light of the Cassegrainian Telescope, compared with that 
of the Gregorian. (Phil. Trans. 1813, p. 206.) 
Having remarked the superiority in the performance of a Casse- 
grainian telescope over those of similar dimensions in the Gregorian 
construction, Capt. Kater made a series of experiments to determine 
the comparative excellence of these two methods of constructing that 
instrument. From a mean of these experiments and from a consi- 
deration of all the circumstances in which they were made, he con- 
cludes that the comparative superiority of the Cassegrainian over the 
Gregorian telescope of equal apertures and magnifying powers, is 
as 20 to 11, or very nearly twice as great. He conjectures that the 
superiority of illumination in telescopes of the former construction 
may possibly depend on their being exempt from the mutual inter- 
ference of rays meeting in the same point, as happens in the Grego- 
rian telescope, when the small speculum receives the rays after they 
have arived at the focus, and after they have become sufficiently con- 
centrated to interfere with each other’s motion. 
2. In a subsequent paper, the experimental research relating to 
the same subject is further prosecuted, and the conclusion arrived at 
is, that the illuminating power of the Cassegrainian telescope, as 
compared to the Gregorian, is in the proportion of 24 to 1. 
3. His next communication to the Society relates to ‘An improved 
method of dividing Astronomical circles and other instruments.” 
The general principle of the method there proposed is the same as 
that of the beam compass; but the apparatus, instead of having points, 
is furnished with two micrometer microscopes, adjustable to different 
distances, as aliquot parts of the arc or line to be divided. Asa spe- 
cimen of the method by which this apparatus is to be used, Capt. 
Kater describes the series of divisions and subdivisions which he 
thinks most convenient in a circle of two feet diameter. 
4. The series of investigations in which Capt. Kater was engaged 
for many years, relative to the pendulum, commences with a paper 
entitled, “‘ An account of experiments for determining the length of 
the Pendulum vibrating seconds in the Latitude of London.” To 
ascertain with exactness the length of the seconds pendulum, an 
object of considerable importance in Physical Science, was scarcely 
