192 S. P. Langley—Comparison of certain Theories of 
On excluding the water and carbonic acid from the two pre- 
ceding analyses, (columns 8 and 4 below,) it will be seen how 
nea rly the original unaltered material resembles that of the 
dolerites (columns 1 sida 2) in tee ar a As usual, there is 
a small difference in the amount of en and in the pro- 
portion between the pyroxene me feldspar. 
1. West Rock. 2. Mt.Holyoke. 3. L. Saltonstall. 4, Durham Mt, 
BieG. sce y BRE 53°54 51°90 51°06 
Alumina ........ 14°29 14°37 16°77 16°35 
Ferrous oxide_.._ 8°30 9°95 10°74 10°79 
Ferric oxide... _- 3°61 1°98 2°00 3°88 
Manganous oxide 44 "45 "39 39 
pet eis S li 9°53 7°83 8°72 
Magnesia -.--- «.j.9tak 6°49 6°31 5°33 
MOGS 204, 250. 2°15 2°60 3°59 2°66 
Picea or *39 *88 75 66 
99°73 99°79 100°28 99°84 
seated one; for so pra uniformity would be well nigh pie 
sible if the source were nearer the surface among the m 
morphic rocks of the crust, as has sometimes been Metin: 
Art. XXIL--On the ge dee vo Certain Theories of Solar 
Structure with Observation ; by S. P. LANGLEY. With a plate. 
In memoirs already published,* allusion has been made to 
the a which would attend studies of the almost unknown 
the umbra of sun-spots, and of forms there 
Sandi owing to the relative darkness, are Aiba nearly unde- 
seribed, and reference has also been made to certain so-call 
eg eepueallliie” shapes seen at times, and which are especially 
oe with large s ae and periods of great disturbance. 
: ulty of seeing cud nenpoe so del- 
its: these “ crystalline ” types have never been m nutely delis eline- 
* American Journal of Science, ‘ioe 1874, Royal pe MGNE: Society’ 
Notices, March, 1874. 
+ Comptes Begun, “May 18, 1874, 
