The surveyor ought to work in solitude. He must no more admit company while mapping than a writer admits visitors to his study while writing. This applies even to geological company, nay, even to the company of a skilled fellow-surveyor... The two authors of this book [Edward Greenly and Howell Williams] once thought that it would be pleasant to have a day's mapping together, and decided to break through their rule. The result was a ludicrous paralysis. The commonest operation seemed a mountain of difficulty. Next day the senior author (whose ground it was) swept an india-rubber over every line and went out again, when, hey presto! And all was clear.