Thomas Stevenson

Prof. Balfour Stewart on Meteorological Research

IT occurs to me to make the following remarks with reference to Prof. Balfour Stewarts proposal in NATURE, vol. xiv. p. 388.

Monolithic Towers of Cement Rubble for Beacons and Lighthouses

IT occurs to me to suggest the trial of common rubble set in Portland or other equally good cement in the construction of beacons and seamarks, as also for lighthouses. The advantages of employing cement rubble, not in prepared blocks but by continuous building, are the following :—

Mode of Masking or Cutting off Sharply the Light from Revolving Apparatus on any Desired Compass-Bearing by means of a Reciprocating Screen

OWING to the optical properties of the lens employed in revolving lights, a formidable element of difficulty comes in the way of effecting a sharp cut-off on a particular bearing; for the direction of the axis of the beam of light which is projected by the lens is being continually changed in the horizontal plane by the revolution of the frame on which it is fixed. So long as the axis of this beam of rays points outside of the line of obscuration the light will not of course encroach on the danger arc, unless to a small extent, when the axis is nearly on the line of cut-off due to the ex-focal rays proceeding from the outer edges of the flame. The light however will begin to be diminished in power from a bearing varying from 12° to 21° outside of the line of cut-off dependent on the size of the lens, the light on the line of cut-off being diminished to the power of one-half. But when the axis crosses that line, then as the rays which come from that part of the apparatus which is still outside of the darkened panes of the lantern is not intercepted by them, the light will begin to be seen within the arc of danger, and as the apparatus goes on revolving the axis will at last point from about 12° to 21° within the danger-arc, according to the breadth of the lens which is employed. Owing to this peculiarity of a revolving light the difficulty of confining the flashes within any required arc of the horizon by means of fixed screens is in fact an insurmountable one.

Note as to Distinguishing Characteristics for Illuminated Buoys

THE plan of illuminating by means of Pintschs system of forcing gas into floating buoys having now been tried by the Trinity House and by the Harbour Authorities of the Tay, I have lately been engaged in considering the best means of distinguishing one buoy from another.

Earthquake in Argyllshire

I BEG to forward to you a letter from the principal light-keeper at Dhu Heartach Lighthouse, addressed to Mr. Cuningham, Secretary to the Board of Northern Lighthouses.

Meteorologic Sections of the Atmosphere

THE primary object of meteorology is to record the pressure, the temperature, the moisture, the electricity, and the movements of the atmosphere. It is desirable, however, that observations on these subjects should be combined with the elements of time and distance. At the general meeting of the Scottish Meteorological Society on June 26, 1867, I proposed the method, since generally adopted, of reducing the intensity of storms to a numerical value by the calculation of barometric-gradients, or in other words by dividing the difference of reading of any two barometers by the distances between the stations where such barometers are placed, thus introducing a nomenclature of universal application, by which the movements of any aërial current, and particularly the wind force of storms, may in every part of the world be reduced to one standard of comparison; and the calculation of thermometric, hygrometric, and electric gradients was subsequently proposed. Since then I suggested to the same society the extension of this system by the establishment of a series of barometers placed at short distances from each other in one or more than one direction in azimuth, so as to give horizontal atmospheric sections for pressure. By means of such lines of section the maximum gradient during storms might, from the nearness of the stations to each other, be ascertained, and thus the phenomena of local storms and other local atmospheric disturbances investigated with some hope of success; and since then a horizontal section extending landwards from the sea-shore has been proposed for temperature and moisture, chiefly with the view of determining the extension inland of the influence of the sea on climate.