[No. 2. 
152 
W. T Blanford — On Birds from Sikkim . 
+ = 1 
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 
in w, 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 w 1 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 alterat ion of external resistance in either 
of the differential branches ? 
[To bo continued.'] 
Notes on a collection of birds from Sikkim, 
by W. T. Blanford, F. G. S.— C. M. Z. S. 
(With Plates VH and VIII.) 
[Received and read 6th September, 1871.] 
Mr. L. Mandelli of Darjiling lias 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 bad 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 mo in the 
