JAN. — MAR. 1858.] 



The Royal Society. 



257 



mountain tour, so delicate an instrument would certainly have 

 come to grief. I took with me four thermometers be Newman, of 

 which one, a B. P. Thermometer, was rendered useless by the 

 mercury setting in the upper bulb, consequent upon expansion of 

 air carelessly left in it by the manufacturer. I have now in all 

 four strong Nutt's Thermometers, in good condition, and two B. 

 P. ditto, one used by Captain William Smyth, R. N. in crossing 

 the borders, and kindly given to us by Colonel Hammerton. 

 These even should the "Adie" be broken, and the instruments 

 recommended, by the Medical Board Bombay not arrive in time, 

 will suffice to determine with tolerable accuracy the altitude of the 

 Unyamisi Lakes. As regards sympisometers, they are found by 

 the long experience of Naval officers, and the accurate hourly ob- 

 servations of a staff of recorders, to be useless by reason of their 

 extreme sensitiveness on this coast within 6° or 8? N. and S. of 

 the Line. This however might not be the case on land. 



For a reference point of known pressure, I am happy to say we 

 can now confidently apply to Zanzibar. Mr. Apothecary Frost, an 

 able and accurate observer, has during the last ten months filled 

 up Meteorological tables with the Barometer, — probably the same 

 instrument sent by the Bombay Geographical Society in 1847, — 

 with Thermometer attached and unattached, wet and dry bulb, 

 evaporating dish, and with the rain gauge. As the Society seems 

 to take an interest in these observations, I have the honor to trans- 

 mit copies with which Mr. Frost has obliged me. 



I now proceed to answer your letter paragraph by paragraph. 



For enquiries into the hydrology of the region which we pur- 

 pose exploring, I shall be careful to provide myself with a dish 

 and a gauge. The professionally learned however must not be 

 exacting in their demands for observation. These African ex- 

 plorations present peculiar difficulties, An expedition into the 

 Eastern Interior is a small campaign, in which the traveller is 

 beset by all the troubles, hardships, and perils of savage warfare. 

 He must despair of studying " infusoria," unless at least he have 

 nothing else to do. 



