( ^44 ) 
alts. The Zodiacal Light is the purer unmixed 
Atmofphere of the Sun : But an Aurora Borealis is 
the Effect of the Solar Atmofphere, confequent upon 
its making a Defcent into, and blending itfelf with 
the Atmofphere of our Earth, at certain Times and 
Seafons of the Year. But a more particular Account 
of this Matter will be given hereafter. 
The learned Author of this Work has taken a great 
deal of Pains in compiling it. He has look’d °over 
the Accounts of Meteors, from the fifth Century- 
down to the prefent Time, in the Hiftorical Part ; 
and has ranged them in very good Order, in regard 
of the feveral Returns of this Phenomenon, making 
fuch Remarks by the way, as ferve to fupport his So- 
lution of it in the Philofophical Part. 
By a Return he does not mean barely a fingle Ap- 
pearance, but a Series of them after a Ceffation or 
Non-appearance for feveral Years. Thus he makes 
but twenty-two Returns from the Year 400 to 1716, 
while the feveral Appearances of thefe Lights from 
1707 to 1710, after a ceafing to be feen for twenty 
Years, are reckoned but one Return. 
Mr. Mairan hopes the learned World will take 
the whole Performance under their Conlideration, and 
give their free Thoughts upon it. 
The Workconfilts of five Sections j the firft gives 
a (hort Hiffory of the Zodiacal Light. In the fe- 
cond he treats at large of the Atmofphere of the 
Earth ; its Altitude, and the ^Height of the Au- 
rora Borealis in it, and the Exclulion this Circum- 
ftance gives to fome of the Caufes, which have been 
already aflign’d, of this Phenomenon. In the third 
he propofes the Caufe, and accounts for the Forma- 
tion 
