152 W. T. Blanford— On Birds from Sikkim. [No. 2, 



^f^^_ / = Q 



gives all that is necessary to determine g and g ', being those values which 

 would make the reading at or near balance most sensitive when a variation 

 hi to, the external resistance belonging to coil g, takes place. 



Now it is clear that equations II and II ' are not necessarily identical, 

 as long as p does not fulfil certain conditions, and therefore the first set of 

 equation II and 1 may give entirely different values for g and g ' from those 

 obtained from the second set II' and I), which means that a simultaneous 

 maximum sensitiveness with respect to an alteration of the external re- 

 sistances to, to' in either of the two differential branches, is not always 

 possible. The following very important and interesting question, therefore, 

 remains to be solved. 



What general condition must he fulfilled in the construction of any 

 differential galvanometer in order to make a simultaneous maximum sensi- 

 tiveness possible, with respect to an alteration of external resistance in either 

 of the differential branches? 



[To be continued.^ 



Notes on a collection of birds from Sikkim, 

 by W. T. Blanford, F. G. S.— 0. M. Z. S. 



(With Plates VII and VIII.) 



[Keceived and read 6th September, 1871.] 



Mr. L. Mandelli of Darjiling has sent to me for determination a most 

 interesting collection of Sikkim birds, together with a few obtained from the 

 plains near the base of the Himalayas. The birds sent are from various 

 elevations, some being evidently from considerable altitudes. Strange as it 

 may appear, after this chosen land of the feathered tribes had been explored 

 and ransacked for years by such ornithologists as Hodgson, Jerdon, Tickell 

 and many others, it yet yields novelties to so energetic a collector as Mr. 

 Mandelli. Amongst the birds sent is a sixth Himalayan species of Propasser, 

 indicated, it is true, some years since by Mr. Blyth, but not hitherto described, 

 and the male of which was previously unknown. There is also a new 

 Pellorneum, and apparently one or two undescribed warblers. Two other 

 birds are additions to the fauna of India, and new localities are furnished for 

 a few others. 



To my notes on Mr. Mandelli' s collection I have added some on birds col- 

 lected by myself at low elevations in Sikkim. In another paper (antea p. 30), 

 I have given a complete list of all the birds observed or collected by me in the 



