426 



Dr. Royston-Pigott on 



[June 19, 



XX. " Observations on the Functions of the Ganglia which are 

 formed in the Posterior Roots of the Spinal Nerves." By 

 Robert Lee, M.D., F.R.S. Received June 19, 1873. 



(Abstract.) 



The author gives a summary of the history of the discovery of the 

 ganglia on the posterior roots of the spinal nerves, and expresses the 

 intention of stating his views respecting the functions of the cervical and 

 thoracic ganglia of the sympathetic nerve and the posterior roots of the 

 spinal nerves in a future communication. 



XXI. " Researches in Circular Solar Spectra, applied to test 

 Residuary Aberration in Microscopes and Telescopes, and 

 the construction of a Compensating Eyepiece, being a sequel 

 to the paper on a Searcher for Aplanatic Images." By G. 

 West Royston-Pigott, M.A., M.D. Cantab., Memb. Roy. 

 Coll. Phys., Fellow of the Camb. Phil. Soc, the Royal Ast. 

 Society, &c, and late Fellow of St, Peter's Coll., Cambridge. 

 Communicated by Prof. Stokes, Sec.R.S. Received April 24, 

 1873. 



The researches detailed in the present paper were commenced in May 

 1871. The results arrived at were largely obtained from using the 

 microscope. Similar but less brilliant and more scanty appearances can 

 be obtained with the telescope; but the very high power and ready 

 adaptability of the former confers some advantages not offered by the 

 latter. 



In both, however, the same principles are illustrated. 



A cone of rays of small angular aperture having the object-glass for 

 its base in each case engages the eyepiece and emerges parallel, and 

 the eyepieces are similar in each. 



Peculiar facilities for studying solar spectra and their indications of 

 aberrations and mechanical errors also are afforded by the former. The 

 focal plane of vision may be employed to examine the effects of the inter- 

 ference of complex cones of light of large angular aperture, at least 

 twenty times larger than those observable by the telescope. 



The subject of the optical contacts of Yenus at the coming transit 

 confers peculiar interest on the nature of accurate definition of the final 

 image presented to the eye-glass, especially as the new parallax will be 

 entirely dependent on the keen definition of the four contacts. 



The discovery by the writer of an unsuspected residuary aberration in 

 the best microscopes, described in the Philosophical Transactions for 1870, 

 renders it probable that some such a residuum still remains in telescopes ; 

 and this might impair the accuracy of such delicate observations as the ap- 

 parent contacts between Venus and the solar limb. Eyepieces, abounding 



