My dear Sir,

I have just received your’s of yesterday, and am very sorry to hear that you are again suffering, and that I cannot have the pleasure of meeting you again before I leave.¹ I trust however to see you at Newcastle.² I shall not neglect to send you copies of all the papers I have published in England in connection with Natural History & Formosa,³ and if you are interested on Chinese topics, (which are normally distasteful to the British mind), I will present you with a copy of my work on the China war.⁴

You are doubtless aware of the cosimilarity of tendency to change of the Japanese as compared with the Chinese birds with the British birds as compared with those of the European continent. The causes are probably due to the influence on the respective atmospheres produced by the Gulf streams of the Pacific and the Atlantic. Whatever the causes the facts are pretty patent. The differences in plumage of several Japanese birds from allied forms on the main has been often noted, but the strongest in point is in the case of the Wagtails. You are acquainted with the instance of the Grey-backed Wagtail (Motacilla alba, L) in England acquiring a black back—the M. Yarellii Gould.⁵ In eastern Asia the same thing occurs in other forms of this group. The grey-backed wagtail of Eastern Siberia, Amoorland, and China, in Japan acquires a black back. The black-backed race was procured and noted by Pallas as a Kamtschatkan variety of M. albeola (Zoograph. Ross. Asiat. Vol I. p. 507),⁶ and has been wrongly referred by modern authors to M. lugubris of western Siberia. In Formosa however where the influence of the gulf stream is strongly felt in the prevalence of rainy weather, the grey-backed is the resident form; though in winter the black-back also occurs, as it does during that season on the China Coast. There is a marked distinction between the two birds, sufficient to distinguish them at first sight; but in my large series of specimens I have one undoubted grey-back with marks here & there of black on its back.

The Budytes group in the east are affected in a similar way to what prevails in Europe. In China, south of Shanghai, the Yellow Wagtail moults in summer into the plumage of typical B. flavas, L. North of Shanghai it adopts the plumage of B. cinereocapilla. In India & Siam that of B. melanocephala. In Japan that of B. rayi of Great Britain. In Formosa similar to B. rayi but with brown instead of yellow cheeks.— In Java & the Archipelago with black cheeks—B. melanotis. Thermally considered the lines of latitude coincide of the areas of the respective forms in the east & west.— Climate in these cases must therefore have something, if not all, to do with the cosimilarity of change. But there are many other like subjects, which will doubtless prove of interest to you have been considered at some length in the different papers I have written, & the shortest way therefore to communicate them to you will be to send you the papers, which I will not fail to do, as soon as they come to hand.

Meanwhile I remain, with hopes for your speedy recovery to health & strength. | Your’s ever truly, | Robert Swinhoe

P.S. I trust you will have no objection to send me a Photograph of yourself in return for mine which I now enclose.⁷ I would esteem it as a great favour. Kindly sign your name at the foot of the Carte. R S.