PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 541 



purity of the sand is of so much importance that the small pro- 

 portion of impurities in sea sand has caused glass works to be 

 removed a considerable distance, from one locality to another. 

 The Lenox glass works were removed from the eastern part of 

 Massachusetts, in order to be near the pure sand found in Lenox. 

 All the sand now used in the glass works of the United States is 

 derived from the older rocks. The Lenox sand belongs to the 

 Taconic system, the very oldest of the fossiliferous rocks. The 

 Oneida county works, the works in Wayne county, and those in 

 Oswego, all use the Oneida county sand, which is derived from the 

 Silurian rocks — the rocks lying next above the Taconic. The 

 Pittsburgh works use the magnesian sand stone of the lower 

 silurian, obtained from Missouri, a little below St. Louis. 



The Chairman. — Will Prof. Scely give us the chemistry of gWss ? 



Prof. Seely. — As it is getting late, and as there are strangers 

 here, prepared to speak, I should like to be excused. 



The Chairman. — Prof. Dwight, of the Law School of Columbia 

 College, has kindly consented to give us the law in relation to 

 the use of light, which, he says, under the decisions at present in 

 force, is a dark subject. 



Prof. Dwight. — It may be of some interest to know what are 

 our legal rights in relation to the use of light; and though, as 

 the Chairman says, the subject on the whole is a very dark one, 

 there are some points which are settled. The only case in which 

 questions could arise in our community is in that of proprietors of 

 adjoining lands. There is one way unquestionably in which/ a 

 man may acquire a right to have a window look out over his 

 neigbor's land : that is, by express grant. And the law is settled 

 that such grant, to be valid, must be made by deed — an instru- 

 ment with a seal. All grants of similar rights in land must be 

 made by a sealed instrument. In case of such grant, the right 

 of the owner of the land must yield to that of the grantee ; so if 

 a person has granted to an adjoining proprietor the right to have a 

 window look out upon his land, he cannot so occupy it by build- 

 ing, or otherwise, as to obstruct the enjoyment of this right. 

 Thus far the law is clear ; no doubt can be thrown upon these 

 points. In England, it is settled that the right to light coming 

 over the land of an adjoining proprietor may be acquired in two 

 other ways. If a man sells a building with a window looking 

 out on a vacant lot, he cannot afterward build upon the lot in a 

 way to darken the window. This is called a right by implied 



