A second important cause for inspection lies in the necessity of always ascertaining with accuracy whether the earth connection is really in a faultless state. The immense significance of the earth connection--the basis, in more than one sense, of lightning protection--having been dwelt upon in the preceding chapter, it is only necessary here to state that, even if perfectly secured at the outset, it is liable to disarrangements. One not infrequent accident causing them is a change in the soil from moisture to dryness, which may be brought about either by altered drainage or long absence of rain. The dangers which threaten a break in the earth connection by altered or improved drainage are of the most serious kind, and likely to become more so from year to year. Not only the soil of our towns and cities, but even that of our villages, and the fields themselves, is getting ever more honeycombed by drain-pipes, until almost every drop of moisture is sucked out of the ground. No doubt the pipes themselves may improve the earth connection, if of iron or any other metal. But very frequently they are of earthenware, in which case they are far more dangerous than useful, even if filled with water. To guard against the danger likely to arise from changes in the drainage, it would be wise to have a thorough examination, by means of the test galvanometer, of all lightning conductors near to or affected by alterations in the drains, whenever completed. The same recommendation may be made as regards cases where the soil has become unusually dry after a long absence of rain. Few persons, except those who have made a study of the subject, can form an idea to what depth such dryness often extends, more especially in sandy and gravelly soils.