( 4010 ) 
light, at an hundred foot di|laQce, and that at an hundred 
and twenty foot diftance I could difcern fome of the words. 
When I made this tryal, its Aperture Cdefined next the Eye) 
was equivalent to more than an inch and a third part of the 
Objett-metalL This may be of fome u(e to thole that (hall 
endeavour any thing in Reflexions ; for hereby they w^ill in 
fome meafure be enabled to judge of the goodnefs Gf their 
Inftruments, &c. 
N. B. The Reader may exped ia the next Month another 
Letter^ which came fomewhat too late to be here inferted i 
containing a table^ calculated by the fame Mr. T^erpton^ a* 
bout the feveral Apertures and Charges anlwering the feveral 
Lengths of thefe Telefcopes. 
EPITOME 
Binas Method! Tangentium Dodloris Johannis Wallijii 
Geom. Prof* Saviliani Oxoni<e 5 alias fufius 6c explicatius ab 
ipfo traditse, hicveroob anguftiam loci compendifafta: : 
InquarumSchematifmisfi forfanliterae qusedam redunda^ 
verint, illasad ea pertinerecenfendas funt, quae in ampliori 
ejufdem Scripto continentur^ hie vcro didi de caufa omit- 
tantur. 
H Abes hie {ClariJJime vir) eorum fummam {fitiBim tr adit am) 
quis fufius fcripferam^ meas de Tangentibus Methodos 
JpeSantia 5 duos potij/imum quibus prajertim utor^ alteram in SpC' 
ciebus^ alteram in Lineis ^ utramque generali forma facile explica' 
bilem. 
Priorem adhibeo Gon.Sc(9:.prop.23,30536546,49,e? pajfim alibis 
hcecefl, 
ExpofithCufvA A^^{put4 Parabola, fig. 4. ) quam in a tangat 
A f, diametro VDA occurrens in ordinatim applieentur <lVj ^ 
DOT curves in 0 ^ tangenti in T occurrens, Ponatur autem V0. = b, 
f^ArzV, FF-{) FD-a, adeoqueDA-vi^yDF-fj-gi; 
Eft (propter ftmilia triangula) rF.DF : : V^, I)J:=,^h. 
Item, fi tangens fit ultra curvam^ DT >" DO s fi citra^ DT<. 
DO: Islempe^ DTs=DO fi intelligatur D in F'^ fed^ f extra 
dT vel DO my or prout tangens ejl ultra citrave curvam. 
