126 MISCELLANEOUS ARTICLES USED IN HORTICULTURE. 



A levelling instrument of some kind is occapionally required in 

 gardens; for example, when box-edgings are to be taken up and re- 

 Fig 100 planted, it is necessary to have the ground of 

 exactly the same level on both sides of the walk, 

 and this can only be done by levelling across. 

 The use of the level implies also the use of poles, 

 borning-pieces, and other articles belonging to 

 surveying, which, as every one who can take 

 levels must necessarily be familiar with, we do 

 not stop to describe. Fig. 100 is a more con- 

 venient form for a garden level than that used by bricklayers ; be- 

 cause, by the curvature on the under-side, the operator can more 

 readily level across raised gravel- walks. 



Thermometers are requisite, more especially where there are plant 

 structures of any description ; and it will be very desirable to have 

 terrestrial thermometers for ascertaining the temperature of the soil 

 in the open garden, as well as of the soil, and of tan or dung beds, 

 under glass. It is true that a knowledge of the temperature of the 

 soil in the open garden will not often enable us to increase that tem- 

 perature, but it will assist us in accounting for particular effects : and 

 sometimes, as in the case of coldness produced from the want of 

 drainage, or from a non-conducting covering repelling the rays of the 

 sun, we have it in our power, by removing the cause, to remedy the 

 evil. To ascertain the temperature of the soil with reference to 

 plants growing in it, the bulb of the thermometer should be sunk to 

 such a depth as may correspond with the great mass of the roots, or 

 between eight inches and a foot. For plant-houses, a registering 

 thermometer is a very desirable instrument, as a check upon the 

 attendants in the absence of the master, and more especially in 

 the night-time. Those of Six used to be considered the best ; 

 they are now, however, largely superseded by Negretti's, and other 

 makers. For experimental purposes no thermometer should be used 

 but those tested by the authorities at some of the Meteorological 

 Observatories. For common garden use most of those sold by re- 

 spectable makers are exact enough. 



An hygrometer of some kind is almost as necessary as a thermo- 

 meter, more especially now, when the importance of keeping the 

 atmosphere of plant structures saturated with moisture to a certain 

 degree is beginning to be understood. Perhaps Daniell's hygro- 

 meter is as good as any for garden purposes. It denotes the degree of 

 moisture in the air with sufficient accuracy, and exhibits the amount 

 in temperature of the dew-point, thus enabling the moisture to be read 

 off as easily as an ordinary thermometer. Regnault's hygrometer is 

 said to possess several advantages over Daniell's, but both of them are 

 somewhat too sensitive and delicate for common use in hothouses. We 

 are indebted to James Glaisher, Esq., for a much simpler mode of 

 measuring the amount of vapour in the air. For this purpose a wet 

 and a dry bulb thermometer are simply placed side by side, and it is 



