66

The constitution of the Irish fertile soils hasnot been ascertained, nor has the average annualquantity of rain been determined here. Indeed,the solution of the question proposed by theAcademy , does not strictly require it should,not having been limited to any particular coun-try: but I should suppose its best soil toapproach to the nature of that of Upsal, thefall of rain being probably between 24 and 28inches. In 1752, which was reckoned remark-ably wet, it was 30| inches in Dublin.

Before I quit the experiments of Mr. Tillet,it will be proper to mention a few made byhim, which seem to invalidate the necessityof the presence of the three simple earths infertile soils.

l m0 * In his 26th experiment he tells us, heemployed only pure sand, such as is used formaking glass, yet corn grew well in it the firstyear, indifferently the second, and nearly failedin the third. Mr. Hassenfraz having repeatedthe experiment in pots unperforated, did not■' find it to succeed even the first year, thereforethe success of Mr, Tillet was owing to the per-foration at the bottom of his pot, through which