Bouck White’s The book of Daniel Drew (1910) is a semi-fictional biography that is sometimes mistaken for an autobiography of American financier Daniel Drew (1797-1879). The book contains two popular sayings:
 
. “To speckilate as an outsider, is like trying to drive black pigs in the dark.”
. “To speckilate in Wall Street when you are no longer an insider, is like buying cows by candlelight.”
 
Both sayings—especially “buying cows by candlelight”—popularize the image that Wall Street is an insider’s game. Drew might have said both of them, but it cannot be confirmed.
 
   
Wikipedia: Daniel Drew
Daniel Drew (July 29, 1797 – September 18, 1879) was an American financier.
 
Google Books
The book of Daniel Drew
By Bouck White
New York, NY: George H. Doran Co
1910
Pg. 367:
Unluckily, I didn’t know of this. I was an outsider now. To speckilate as an outsider, is like trying to drive black pigs in the dark. So I kept on selling Erie short just when Gould and Fisk had turned and were buying Erie for a rise.
Pg. 423:
To speckilate in Wall Street when you are no longer an insider, is like buying cows by candlelight.
   
Google Books
Jay Gould:
The story of a fortune
By Robert Irving Warshow
New York, NY: Greenberg
1928
Pg. ?:
Of his fall, he had this to say, “To speculate in Wall Street when you are no longer an insider is like buying cows by candlelight.” Of Jay Gould his only comment was, “His touch is as death.”
   
Google Books
The story of Wall Street
By Robert Irving Warshow
New York, NY: Blue Ribbon Books
1931, ©1929
Pg. ?:
Most of them learn sooner or later that old Daniel Drew was right when he said, “To speculate in Wall Street when you are not an insider is like buying cows by candlelight.”
 
Google Books
Gould’s millions
By Richard O’Connor
Westport, CT: Greenwood Press
1973, ©1962
Pg. 82:
In 1875 he went into bankruptcy, sadly admitting, “To speculate in Wall Street when you are no longer an insider is like buying cows by candlelight.” Four years later he died broke, his estate consisting of a watch and chain, a sealskin coat, a number of Bibles and hymn books.
   
Google Books
The dark genius of Wall Street:
The misunderstood life of Jay Gould, king of the robber barons
Author: Edward Renehan
New York, NY: BasicBooks
2005
Pg. 78:
He (Daniel Drew —ed.) once told Gould that to speculate on Wall Street without inside information made as much sense as to drive black pigs in the dark.