JOURNAL AND PROCEEDINGS. 103 
able. The moon’s disk subtends an angle of about half a degree, 
and mapping the lunar surface into 360 degrees of latitude and longi- 
tude, a lunar degree at the centre of the disk measures nearly 19 
miles. Little that man has wrought on earth, could his most gigan- 
tic work be transferred to the moon, would attract much if any notice 
at the earth’s distance, though if man’s handiwork would pass un- 
noticed, no important lunar formation could now disappear or be 
materially changed, and elude detection. At the centre of the moon’s 
disk, one second of arc equals 1.1585, more than one and a tenth 
English miles. What portion of the star-sphere a second of arc 
covers may be realized by calling to mind, a linear foot subtends a 
second of arc at 39 miles distance, and that the pole-star and its com- 
panion are 18 seconds of arc apart. 
In the present stage of research there is divergence of opinion 
on many questions of lunar physics, though not more than might be 
expected from independent investigation. Bessel estimated the 
moon’s atmosphere to be a thousandth the density of that of the 
earth, while Neison considers it to be greater than Bessel’s estimate. 
Nasmyth, on the other hand, concludes that the moon is devoid of 
water, atmosphere and soil, and excepting contraction and expansion 
of the lunar crust from change of temperature, he thinks the moon 
now undergoes but little change. That there is great variation of 
temperature on the moon’s surface from exposure for half a lunation 
to the sun, and from radiation of lunar heat into space for a like 
period admits of no doubt. The six foot speculum of Earl Ross’ 
great telescope was, some years since, used for investigating the 
probable temperature of the moon. Earl Ross considered his 
researches tentative, and results approximate only. From his ex- 
periments and observations it was concluded that the difference 
between maximum and minimum temperature at the moon’s surface 
is 200 degrees Centigrade. This difference in temperature between 
lunar mid-day and midnight was computed from measurement of 
the moon’s radiant heat. This agrees in part with Sir John 
Herschel’s estimate of the moon’s climate. He writes: “The lunar 
“day is one of unmitigated burning sunshine, fiercer than an 
“equatorial noon, continued for a time equal to our fortnight, and 
“the lunar night is a period of the keenest severity of frost, exceed- 
“ing that of our polar winter, and of the same length as the 
“lunar day.” 
