30 L. CASELLA'S CATALOGUE 



stronger portion of the wheelwork ; it has holes on the flange for screws or 

 nails, by which means it is easily fixed to the roof of a house, or to a pole 

 placed in a garden, or field, or hy the seaside. The chains (e e) act on 

 improved rollers, over which they cannot pass without turning them, and 

 are brought into connection with the clockwork and registering parts, placed 

 in a room or box for protection, at any vertical distance from the base (d), say 

 from three to twenty-five feet. In size, the height of the upper part is 

 thirty-nine inches from the base of the box (d], the diameter over the cups is 

 twenty-four inches, and its strength and general construction such as to bear 

 the vicissitudes of the severest storm. Where frequent absence is requisite, 

 or in places of difficult access, the little attention required in using this 

 instrument can hardly be over-estimated. A small dial showing time, and 

 another the direction, is also attached to the self-recording apparatus in the 

 room. The action of each one is tested and guaranteed to give the same rate 

 of speed as that of the standard anemometer constructed by L. CASELLA for 

 the Kew Committee and other Observatories belonging to the Government 

 (fig- 80) p. 28 . 38 



82. Enlarged Anemometer, or Anemograph; for harbours and public observatories, 



as recently constructed by L. CASELLA for the Kew Observatory and the other 

 observatories of the Meteorological Office of the Government. In this arrange- 

 ment the cups revolve in the same manner as in the smaller instrument, but 

 the registration is obtained by means of a revolving cylinder to which paper is 

 attached, and the direction as well as velocity is continuously shown for every 

 minute of time by means of a clock which forms part of the instrument. The 

 exposed portion of this anemometer may be placed at any height, whilst the 

 registering part is kept in a room or other covered place for observation. For 

 the purposes of comparison, the registering papers supplied with these anemo- 

 meters are similar to those used with the Government instruments, several 

 more of which are now being erected (fig. 82) p. 29 . 70 



83. ENLARGED ANEMOMETEE, or ANEMOGBAPH, if made to register in a lower room 



of the building . . . . . 75 to 80 



84. Anemoscope^ or Dr. Halleui^s Portable Wind Vane, for travellers, with compass, 



bar needle, etc., showing the direct course of the wind to half a point of the 

 compass (fig. 84) p. 31 . . : . . . . 220 



85. Casella's Hypsometer, for measuring mountain heights by the vapour of boiling 



water. The improvements effected in this instrument by L. CASELLA render 

 it the most certain and portable means we have of measuring great elevations. 

 The thermometer, strong, with small bulb, is divided and figured on the stem, 

 and is sheltered from cold when in use by a double telescopic chamber, into 

 which it is placed to any required depth through a loose piece of india rubber, 

 which rests on the top. The proper depth is, with the bulb, not quite so near 

 the water as is shown in the sketch. The chamber being filled with vapour 

 from the boiling water beneath, and the inner chamber and tube thus enveloped, 

 the vapour descends in the outer chamber, and escapes by the outlet. By this 

 means the mercury, both in the bulb and stem, is immersed in pure vapour, 

 whatever kind of water may be employed ; less than a wine-glass full of 

 water and half as much spirits serve for several observations. The therm o- 



