728 REPORT—1896. 
According to this theory, the sailing bird derives its energy from fluctuations 
in the resolved part of the wind-velocity, at right angles to the bird’s course. 
Such side winds would, in particular, be brought into action first on one side and 
then on the other whenever the bird passed through the centre of an atmospheric 
vortex. The exact part played by variations of wind-velocity 7” the direction of 
the bird's course is more difficult to understand, but it seems improbable that such 
variations alone could account for the phenomena. If the bird were moving 
slowly enough to receive the wind sometimes in front and sometimes from behind, 
it would at intermediate instants be at rest relative to the wind, and would then 
obtain the minimum degree of support. Ifit were moving rapidly through the 
air, the latter would always strike the bird in front, so that its horizontal ‘motion 
would be constantly retarded. 
Anyone watching a flock of birds will observe that they often actually are 
carried up by a sudden side-gust of wind in the manner here described, showing 
that if this is not the only cause of the phenomena presented by the sailing bird, 
it is at any rate one of the causes. So much has been written on the subject that 
it is impossible to say how far these remarks may have been anticipated ‘by other 
writers; but I think they may help to clear up some of the difficulties which have 
been experienced in accounting for the sailing flight of birds. 
11. On the Stanhope Arithmetical Machine of 1780. 
By the Rev. R. Haruey, W/.A., FBS. 
12. The Exploration of the Upper Air by means of Kites, 
By A. LAvURENCE Rotcu. 
This is a preliminary account of experiments being conducted at the Blue Hill 
Meteorological Observatory, Roadville, Massachusetts. The author, after referring 
to previous instances of the use of kites for meteorological purposes, gives details of 
the apparatus and methods employed at Blue Hill in kite observations, which were 
commenced in 1891, and are still being carried on. The kites are, some of 
trapezoidal, and some of Hargreaves’ cellular, form, and are controlled by pianoforte 
wire of 300 lb. tensile strength. The pull on the wire is not allowed to exceed 
125 lb. Two self-recording aluminium instruments are used, one recording, on a 
single cylinder, barometric pressure, temperature, and humidity. The other records 
temperature, humidity, and wind-velocity. 
Each is suspended between two kites to diminish oscillation. 
As an illustration of the importance of the use of kites in weather prediction 
may be mentioned the fact, which has been demonstrated at Blue Hill, that in the 
United States, at least, warm and cold waves commence in the upper regions before 
they are felt at the ground. The conditions at mountain stations only approximate 
to those prevailing in the free air. Kites are superior to captive balloons, as being 
both cheaper and capable of flying through a greater range of wind velocity, and to 
greater altitudes. 
TUESDAY, SEPTEMBER 22, 
The following Reports and Papers were read :— 
1. Interim Report on Electrolysis and Electro-chem try.’ 
See Reports, p. 230. 
2. Report of the Electrical Standards Committee—See Reports, p. 150. 
