[ 6 73 3 
he had fomething elfe in View : but in many Gafts 
the Chemifts 'complain, that, having once acciden- 
tally light on a curious Experiment, upon endea- 
vouring to repeat it, they have never been able to 
make their Procefs fucceed exactly, as it did the 
firft time, notwithftanding that they made ufc of 
the fame Materials, in the fame Quantity, and con- 
ducted the Procefs thro* exactly the fame Operations. 
Where then mult the Gaufe of the Mifcarriage lie > 
Surely in the Degree of Heat made ufe of in the 
two Experiments : For, in many common Opera- 
tions, how ufual is it for a Preparation to be fpoiled 
either by too little, or, in oft commonly, by too 
much Fire, too long or too fhort a time applied ! 
In order therefore to prevent thefe many Mifcar- 
riages, I would advife the Chemift, in his Ope- 
rations, to obferve his Clock with as much Exaft- 
lids’ as. the Aftronomer doth in his Obfervations $ 
and in order to know to a Certainty the very De- 
grees of Heat he ever made ufe of in any Procefs, 
that fo he may be able to repeat and continue the 
fame again in any Repetitions of the fame Experiment, 
let him have his Laboratory furniflfd with various 
Sorts of Thermometers, proportion’d to the Degree 
of Heat he intends to make ufe of. He will find 
thefe Inftruments as ufeful to him in his Proceffes, 
as they have proved to the curious Gardener in his 
Stoves, who by them is taught to keep his Plants in 
the fame Degrees of Heat, as are natural to them in 
their refpe&ive Climates 5 which hath been fet forth 
in Tables, after a very ingenious manner, by Mr* 
S fff a Sheldrake 
