Boart Longyear diamond drilling firm; Brainard-Kilman, a maker of civil engineering devices, such as well monitoring and test equipment; and ChemGrout a mfg of cement grouting equipment. Longyear acquired Slope Indicator Company, the nation's largest producer of geotechnical instruments, and Northern Air Supply in 1988, followed by the Campbell Pacific Division in 1989 and WTD Environmental Drilling in 1990. Then in 1994, North Star Drilling Company, specializing in sonic drilling was acquired. On January 2, 1995, Boart International and the Longyear Company officially merged into a single company and changed its name to Boart Longyear Limited. At this point the two companies
Léon Teisserenc de Bort an indication of a temperature inversion or at least of a zero lapse rate above this altitude. For many years he was uncertain whether he discovered a true physical phenomenon or whether his measurements suffered from a systematic bias (indeed, the first measurements "did" have a positive temperature bias as the instruments were liable to radiative heating by solar radiation). That is why Teisserenc de Bort carried out 200+ more balloon experiments (with a substantial part of them being held during the night to eliminate radiative heating) until 1902, when he suggested that the atmosphere was divided into two layers.