Description of the Coming-up Glass Telescope. 319 



and rools, through the bark, has been intercepted : and why 

 some portion of alburnous matter is in all trees* generated 

 below incisions through the bark. 



It was my intention this year to have troubled you with 

 some observations on the reproduction of the buds and 

 roots of trees ; but as the subject of the paper, which I have 

 now the honour to address to you, appeared to be of more 

 importance, I have deferred those observations to a future 

 opportunity; and I shall at present only observe, that I 

 conceive myself to be in possession of facts to prove that 

 both buds and roots originate from the alburnous substance 

 of plants, and not, as is, 1 believe, generally supposed, from 

 the bark. 



I am, &c. 



Elton, Dec. 4, T. ANDREW KnIGHT. 



1804. 



XLVI. Descriptioji of the Coming-up Glass Telescope, as 

 made hy Mr. Thomas Jones, Mathematical, Optical, 

 and Philosophical Instrument Maker ; Pupil of the late 



Mr. R.-VMSDEN. 



jf\.s it is of much importance, especially in war time, du- 

 ring the chase of a vessel, that the chasing ship should be 

 able to ascertain whether she lessens or increases her di- 

 stance from the object of which she is in pursuit, I am per- 

 suaded the philosophical world will be pleased with a de- 

 scription of an instrument adapted to this useful purpose, 

 invented by the late Mr. Ramsden. It consists in applying 

 a micrometer to a refracting telescope of about two feet 

 long, or to a day and night telescope ; and I have been in- 

 formed by some who were furnished with them by Mr. 

 Ramsden, (and by myself since his death,) that they an- 

 swer the purpose remarkably well. 



To this combination the English sailors have given the 

 name of a coming-up glass. To fit the telescope for this 

 use, the third glass from the eye, in the drawer of the tele- 

 scope, is divided in two by cutting it across its centre at 

 right angles to its surface ; and, in using it, these two semi- 

 lenses are separated from each other in the direction of their 

 line of separation. By turning a finger-screw on one side 



* 1 have in a former paper stated that the perpendicular shoots of the vine 

 form an exception. I spoke on tlie authority of numerous expcrimenis ; but 

 they had been made late in the summer ; and on repeatinir the same experi- 

 ments at an earlier period, I found the result in conformity widi my experi- 

 ment) on other tree«. 



X2 of 



