353 



9. Sir George Shuckburgh Evelyn had, in the course of his inquiries 

 respecting a standard of weights and measures, examined with great 

 care the weights of a standard cube, cylinder, and sphere, and the 

 methods employed for this purpose had been minutely described; 

 but the mode of ascertaining the dimensions of these bodies had not 

 been so fully detailed. Capt. Kater was accordingly desirous of re- 

 investigating this latter branch of the subject before the Commis- 

 sioners of Weights and Measures should make their final report. The 

 apparatus he employed for this purpose, and the results of his ex- 

 periments, are stated in a paper also published in the Philosophical 

 Transactions for 1821. 



10. These researches were continued by Capt. Kater in the year 

 1825; and the details are given in a paper published in the Phil. Trans, 

 for 1826, and entitled " An Account of the construction and adjust- 

 ment of the new standards of weights and measures of the United 

 Kingdom of Great Britain and Ireland." 



11. The series was completed in 1830 by the account he gives of 

 the detection of a source of error in estimating the standard of linear 

 measure, arising from the thickness of the bar, on the surface of 

 which the lines are traced, and of the means he took to obviate it. 



12. The attention of Capt. Kater was at one time directed to the 

 ascertaining the best kind of steel for the construction of a compass 

 needle, the most advantageous form to be given to the needle, and 

 the most effective mode of communicating to it magnetism. Many 

 curious and unexpected results were obtained in the course of this 

 investigation. 



13. A remarkable volcanic appearance in the moon being observed 

 by Capt. Kater in February 1821, he communicated to the Society 

 shortly afterwards an account of the phenomenon, which was pub- 

 lished in the Phil. Trans, for the same year. 



14. One of the greatest benefits conferred onscience by Capt. Kater 

 was his invention of the floating collimator, an instrument of which 

 the object is to determine the situation of the line of collimation of 

 a telescope attached to an astronomical circle, with respect to the 

 zenith or the horizon in any one position of the instrument ; or in 

 other words, to determine the zero-point of the divisions on the limb : 

 an operation which was before usually performed by the use of the 

 level or the plumb-line, or by the reflexion of an object from the 

 surface of a fluid. Each of these methods was liable to many in- 

 conveniences and defects ; all of which are avoided in the floating 

 collimator. The principles on which this instrument is constructed 

 are two ; the first is the property of a telescope employed by Gauss, 

 and subsequently by Bessel, in virtue of which the cross wires of a 

 telescope adjusted to distinct vision on the wire, may be distinctly 

 seen by another telescope also similarly adjusted, at whatever distance 

 the telescope may be placed, provided their axes coincide ; in which 

 case the rays diverging from the cross wires of either telescope, will 

 emerge parallel from its object-glass, and will therefore be refracted 

 by that of the other telescope to its sidereal focus, as if they came 

 from an infinite distance. The other principle, which is employed 

 as a substitute for the common level, is the invariability with respect 



