552 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



15. Winter Spray for American Blight (Bunyard). — Wherever this 

 preparation came in contact with American blight it proved deadly to 

 this pest. It is a perfectly safe spray. 



16. Winter Spray (Voss). — A wash for cleansing trees of lichen and 

 destroying pests, &c, on the trees. It acted fairly well. 



17. Woburn Paraffin Emulsion (Voss). — This wash seemed too 

 powerful at the strength recommended. 



18. Wood Oil (Boor). — This is an oily extract from wood, and is made 

 in Sweden. It preserves the wood, without in any way discolouring it, 

 and causes the "grain " to be more marked. 



19. Wonderful Fertiliser (Voss). — A very good all-round manure. 



20. Vaporiser (Voss). — An ingenious little apparatus for producing 

 sulphur fumes to kill mildew, with no risk of burning. 



21. Horticultural Hygrometer (Negretti & Zambra.). — No meteo- 

 rological question is of greater interest to the gardener than 

 that of forecasting night frosts. It has been stated that the minimum 

 temperature recorded on any night is an approximation to the dew- 

 point temperature of the preceding evening, and that, consequently, the 

 likelihood of frost occurring during the night can be ascertained by 

 observing whether the evening dew-point temperature is above or below 

 32 F. Actually, the minimum reading on the grass is generally lower 

 than the dew-point. Indeed, while frost may be expected with certainty 

 if the dew-point temperature be 32° F. or less, it may also occur however 

 hot the preceding day and with an evening dew-point much above 32° F. 

 provided the sky be very clear. Radiation on a brilliant night may 

 cause a rapid fall of surface-temperature from 60° at 9 p.m. to 30° 

 before sunrise. Messrs. Negretti & Zambra have introduced a simply 

 designed rust-proof instrument, containing wet and dry bulb thermometers 

 and a central revolving drum graduated to indicate the probability of 

 approaching frost, the method of graduation being based on a long series 

 of observations, and the readings requiring no calculation on the part of 

 the observer. The lowest (black) section of the drum, including all cases 

 when the dew-point temperature is 32° or less, indicates "frost may 

 be probable." The topmost (white) section indicates " frost highly im- 

 probable.". An intermediate (shaded) band, occupying an increasing 

 proportion of the area of the drum as the difference between wet and 

 dry bulb readings increases, indicates "frost doubtful." The instrument 

 was tested at various hours on a long series of evenings, but very seldom 

 gave a different forecast for the night from that likely to be given by the 

 average gardener observing the brilliance of the sky and the degree to 

 which it was overcast, and the direction of the wind. Unfortunately a 

 change of weather is as little foreseen by the thermometer as by the 

 observer, and the instrument is of no value in forecasting changes of 

 weather similar to the following. On the evening of November 5, with 

 a dull, overcast sky and a very light easterly wind, almost calm, the 

 minimum for the evening was reached at 7 p.m., when a self-recording 

 thermometer in a screen one foot above the surface of the ground 

 registered 42'7° F. At 11.16 p.m. the dry bulb of the horticultural 

 hygrometer (exposed) read 46°, the wet bulb 45°, and the radiation 

 thermometer on the grass gave the minimum reading 36° from earlier 



