XXV111 
PREFACE. 
lived near a convenient fpot for the ex- 
periment, to open a place where a great 
number of Sand-Martins had been ob- 
ferved to build their nefts in the foregoing 
fummer. The earth was accordingly 
opened near the edge of a pit where 
many of their holes were made; and, on 
digging down to them, no birds were 
found ; though the nefts were found per- 
fect, in fome of which were found cor- 
rupted white eggs, and in others fome 
flies of the Bee kind had taken fhelter. 
To be the more certain, the paftages into 
the nefts, which were about a foot and a 
half in length, little more or lefs, were quite 
free of any lodgments of birds ; and, up- 
on fearch, were found to be open and 
empty : many of the holes were examined 
and traced to their utmoft extent, and no 
birds were found in them. 
Colours require a certain degree of 
light to fhew them in their greateft per- 
fection, and make appear their proper 
diftindions one from another : for, as the 
light declines to darknefs, all colours are 
loft in the fable hue; and, if light be 
increafed to the higbeft degree, by bring- 
ing the fun’s rays to a point through a 
convex glafs, and that light be thrown 
on bodies of various colours, they will all 
appear the fame, the excefs of light 
wholly overcoming the colours. Vid. Hift. 
de l’Acadcmie de Paris, an. 1711, 
The exceftes of heat and cold have, 
in fome inftances, near the fame efied ; 
lire bliftei s the fkin ; and, in the coldeft 
leafons at Ifudfon’s Bay, and in the 
northern parts of Europe, the touch of 
cold iron, &c. is dangerous : for metals, 
by their greater gravity, are, in propor- 
tion, colder than frozen water; and, if 
touched by the hand, will blifter and 
ecclefiajlique de fes intimes amis, qui derncare 
dans le voifnage d'une pldce propre a cette 
experience , de fair e creufer dans unjndroit 
oil Ion avoit vu un grand nombre de Mar- 
tinets faire leurs nids durant Pete precedent . 
On a done ouvert la terre pres du penchant 
d'une fojje, oh Us avoient fait beaucoup de 
trous ; ct, en cr enfant jufquaux nids, on ny a 
point trouve d'oijeaux, quoique les nids fe foient 
trouves parfaits : ily avoit dans quelques tins 
de ces nids des aeufs blancs pounds , et dans 
d' autre s tl setoit refugie des mouches a mieh 
Pour rendre la chofe encore plus certatne , on 
a examine tries exatlement les pafages qui con - 
dui foient aux mds, et qui etoient environ d'un 
pied et dam de long , on les a trouves ouvert s et 
vuides : en fin , on a examine et trace d'un 
bout d V autre plufcurs trous , fans y tr Oli- 
ver d'ofeaux . 
Les couleurs demandent un certain degre de 
htmiere pour fe faire voir dans t cute lour per - 
fetlion, et pour montrer ce qui les diftingue 
proprement les unes des autres : car, comme la 
lumiere decline et fe change en tenebres , de 
me me toutes les couleurs fe per dent dans le mlr ; 
et, ft Ion augmentoit la lumiere au plus bant 
degre pofible , en reduifant par 'le moycn d'un 
verre convexe tout les rayons du fioleil a un 
point , et que Von fit tomber cette lumiere fur 
des corps de diver fes couleurs, ils paroitroient 
touts de la mane couleur , parce que I'exces de 
la lumiere abforbe end ere meat les couleurs 
Ily a des cas oh I'exces du froid et du chan a 
produifent le me me efifet : le feu cayfe des em- 
poulcs a la pcau ; et, d la Baye de Iludfon , 
de mane que dam les parties feptentrionales de 
! Europe, il ejl danger eux de toucher d du fi'er 
froid : car les metaux font plus f olds que la 
glace , d proportion de leur gravite ; et, Ji cn y 
* Voi. PHift. de PAcadL des Sciences de Paris, pour 
l'annee 17 
