Bregazzi hothouse thermometer

1935. Bregazzi's hothouse thermometer (fig. 526.) has a double back (b, c); the ad-vantage of which is, that, when hung from the roof of the hothouse, the heat of the sun is prevented from operating on the back of the bulb (d), by the current of air which passes between the backs. (Gard. Mag., vol. iii. p. 215.)