■I 703 ) 
fatisfaaion if he a little change the method which he has pro ^ 
pounded, and inftead of a multitude of things try ©nly the Ex- 
feriwientum Cancis, For it is not number of Experiments , but 
weight to be regarded ; and where one will do, what need 
many? 
Had I thought more requifite^ I could have added more ; 
For before 1 wrote my firft Letter to you abouc Colours, i 
had taken much pains in trying Experiments about theihj and 
written a Traflateon that fubjffl 3 wherin I had fee down at 
large the principal of the Experiments I had cried ^ amongft 
which there happened to be the principal of thofe Experi- 
ments which Mv.Lucas has now fent me. And as for the Expe- 
rimeuts fet down in my firft Letter to you, they were only fuch 
as I thought convenient to feleft out of that Tra date. 
But fuppofe thofe had been my v\ hole ftore , yec Mr. Lu€<m 
Ihould not have grounded his difcourfc upona fuppofition of 
my want of Experiments, till he had examined thofe few. For 
if any of thofe be demonflrative,they will need no affiftants^nor 
leave room for further difputing about what they demonftrate. 
The main thing he goes about ro examine is, the different re- 
frangil^ilitjf of Lights And this I demonftratedby the Expe* 
rimtntum Crucis. Now if this demonftration be good , there 
needs no further examination of the thing; if not good, the 
fault of it is to be fliewn : for the. only way to examine 
a demonftrated propofition is, to examine the demon- 
ftration. Let that Experiment therefore be examined ia 
the firft place, and that which it proves be acknowledged, and 
then if lAt 'Lucas want my affiftance to unfold the difficulties 
which he fancies to be in the Experiments he has propounded^ 
heChall freely have it; for then I fuppofe a few words may 
make them plain to him: whereas, fhou Id I be drawn from de- 
monftrative Experiment to begin with thofe, it might create us 
both the trouble of a long difpute, and by the multitude of 
wordsj cloud rather than clear up the truth. For if it has al* 
ready coft us fo much trouble to agree upon the matter of faft 
in the firft and plaineft Experiment, and yet we are not fully 
agreed ; what an endlefs trouble might it create us, if we fliould 
give our felvesup to difputeupon every Argument that occurs, 
and what would become of Truth in fuch a tedious difpute ? 
Zz2z The 
