«90 Remarks on M. Burckhardt's Contrivance 



declare himself the protector of the purity of the Negrete 

 race, will also, it is most earnestly to be hoped, induce his 

 majesty to extend the same protection to the newly arrived 

 Paulars ; by this measure, and by this alone, the public will 

 be effectually guarded against all danger of the admission of 

 impure blood, which the avarice of ill-judging individuals, 

 seeking alter a premature improvement of the carcase, has 

 too often, it is feared, introduced into our English flock.-. 

 Thus protected, the twofold treasure obtained for the advan- 

 tage of his subjects by his majesty's wisdom and foresight, 

 will become a perennial fountain of true Merino blood, to 

 which those agriculturists who are wise enough to adopt the 

 breed may from time to time resort, to correct their errors 

 if they fall into bad practices, to carry on their crosses, if 

 any such are found to be advantageous, to the highest degree 

 of perfection, and to restore the originality of their stock,, 

 if, in consequence of any unsuccessful experiment, it should 

 have suffered deterioration. 



LI. Remarks on M. Burckhardt's Contrivance for shorten- 

 ing Reflecting Telescopes ; with a new Method of making 

 Refracting Telescopes with a Tuhe only one-third of t/u 

 focal Length of the Ohject- glass. By David Brewster, 

 LL.D. F.R.S., and F.A.S., Edin. 



DEAR SIR, * 



In the Conjiaissancc des Terns for 1809, I observe the de- 

 scription of a new telescope, invented by the celebrated M- 

 Burckhardt, of an intermediate nature between the Gregorian 

 and Newtonian telescopes; and requiring a tube only halt 

 as Ions: as other instruments of the same focal length. The 

 large concave speculum AB, Fig. I, (Plate IX.) is perfo- 

 rated as in the Gregorian telescope, so that the diameter of 

 the aperture ef may be half the diameter AB. The parallel 

 rays Rm, R//, which, after reflection, would have formed 

 the image atF, are intercepted by a plane speculum C, per- 

 pendicular to the axis of the telescope, and of the same size 

 as the aperture ef and are reflected back to the point o, 



whepf 



