Derangement in the Greenwich Mural Circle. 355 



Hal quills are wliite, with the tips and base black ; the remain- 

 der, together with the lesser quills, are black with white tips ; 

 the Tail is nearly hid by its covers, and just exceeds the 

 length of the wings when closed ; the feathers are fasciculated, 

 very short, and fawn-coloiu'ed, transversely marked with waved 

 bands of dark ferruginous, edged with black. Spurious quills 

 black. Of the tinder plumage, the chin is nearly white, chang- 

 ing gradually to ferruginous ; each feather on the neck and 

 breast being spotted with wliite, which spots possess the sin- 

 gularity of being in some lights almost invisible, but in others 

 of a pure shining snowy whiteness; from the breast to the 

 vent all the plumage is white. Legs yellow, one inch and a 

 quarter from the naked part of the thigh to the heel ; all the 

 toes are cleft to the base, and the inner one smallest. 



The birds of this genus have such a general resemblance in 

 the markings of their variegated plumage, that a minuteness of 

 description, although objectionable on most occasions, here be- 

 comes absolutely necessary. 



This description was framed from a specimen belonging to 

 Mr. Leadbeater, who received it from Africa ; another I have 

 since seen hi the well-known Museum of Mr. Brookes. 



LXXI. A Letter from John Pond, Lsq. Astronomer Royal, 

 to Sir Humphry Davy, Barf. President of the Royal Societi/, 

 relative to a Derangement in the Mural Circle at the Royal 

 Observatoiy* . 



My dear sir, — Ihe interest which the Royal Society has 

 always taken in every thing relating to this Observatory, and 

 to which may be attributed its present prosjicrous condition, 

 will, I trust, render unnecessary any apology for this commu- 

 nication. 



I wish to make known to astronomers, as soon as possi- 

 ble, a derangement that has for some time past existed in the 

 mural circle, and of which I have not, till lately, been able to 

 ascertain the cause with certainty. 



This derangement began, I believe, about the autumn of 

 the year 1819 ; the jiosition of the telescope was then changed ; 

 and from that time the error has been gradually increasing 

 till last summer, when the cause was distinctly ascertained, 

 and the proper remedy apjilied. 



In tlie Preface to the Greenwich Observations for the year 

 J8'20, now printing, I shall have an opportunity of stating the 



* I-'rom the Pliilosuphicul Transiic lions, Pait I. for 18J-\ 



Y y 2 amount 



