328 Sympathetic Inks. 



of the day, there was no difcuffio'n. Lalande himfelf mu(? 

 have been aware, that as the introduction of this innovation 

 found, even in France, and particularly in the provinces, fo 

 great oppofition, it would meet with much more in other 

 countries. It would alfo hardly find admiffion among thofe 

 who have ftill any regard for inftitutions which, thoufands 

 of years ago, the firft law-givers and aftronomers declared 

 to be proper for civil life, and which have fince been re- 

 tained through all ages. Befides, this new French calen- 

 dar, in making the year begin at the entrance of the fun 

 into the equinoctial point, determined by aftronomical cal- 

 culation, brings it back upon no folid and fure grounds ; 

 while we, on the other hand, by the very fimple method of 

 intercalation, can determine common time backwards and 

 forwards for many centuries, and differ only one day from 

 aftronomical time in the courfe of 3200 years." 



The Elector of Saxony has enriched the obfervatory at 

 Leipfic with a considerable number of aftronomical inftru- 

 ments, which were before preferved in the mathematical 

 hall at Drefden. 



SVMPATHETIC INKS. 



On this fubject a correfpondent has fent us the following 

 communication : 



" Many receipts have been already publifhed for making 

 inks, the writings with which remain invijible till brought 

 forth- by heat; but many inconveniences attend even the beft 

 of them. Having tried all I have been able to meet withj 

 I have found that fome require fo much heat that the whole 

 paper is fcorched before the letters make their appearance; 

 that in fome the letters are indiftinct when produced ; and 

 that in others the words are almoft legible before the heat is 

 applied. In the courfe of my experiments on this Subject, I 

 hit upon a very fimple mixture which obviates thefe incon- 

 veniences ; as the writing done with it is perfectly invifible 

 till heat be applied, and becomes very black with fuch a de- 

 gree 



