d；　his　head　muffled　up；　all　his　body　tightly　wrapped　in　a　thick　felt　cloak；　crawled　along　the　ground。 He　could　breathe　down　there；　when　the　air　was　pure；　and　with　his　right　hand　he　waved　above　his　head　a　blazing　torch。　When　the　firedamp　had　accumulated　in　the　air；　so　as　to　form　a　detonating　mixture；　the　explosion　occurred　without　being　fatal；　and；　by　often　renewing　this　operation；　catastrophes　were　prevented。　Sometimes　the　'monk'　was　injured　or　killed　in　his　work；　then　another　took　his　place。 This　was　done　in　all　mines　until　the　Davy　lamp　was　universally　adopted。 But　I　knew　the　plan；　and　by　its　means　I　discovered　the　presence　of　firedamp　and　consequently　that　of　a　new　seam　of　coal　in　the　Dochart　pit。〃

All　that　the　old　overman　had　related　of　the　so…called　〃monk〃　or　〃fireman〃　was　perfectly　true。 The　air　in　the　galleries　of　mines　was　formerly　always　purified　in　the　way　described。

Fire…damp；　marsh…gas；　or　carburetted　hydrogen；　is　colorless；　almost　scentless；　it　burns　with　a　blue　flame；　and　makes　respiration　impossible。 The　miner　could　not　live　in　a　place　filled　with　this　injurious　gas；　any　more　than　one　could　live　in　a　gasometer　full　of　mon　gas。 Moreover；　fire…damp；　as　well　as　the　latter；　a　mixture　of　inflammable　gases；　forms　a　detonating　mixture　as　soon　as　the　air　unites　with　it　in　a　proportion　of　eight；　and　perhaps　even　five　to　the　hundred。　When　this　mixture　is　lighted　by　any　cause；　there　is　an　explosion；　almost　always　followed　by　a　frightful　catastrophe。

As　they　walked　on；　Simon　Ford　told　the　engineer　all　that　he　had　done　to　attain　his　object；　how　he　was　sure　that　the　escape　of　fire…damp　took　place　at　the　very　end　of　the　farthest　gallery　in　its　western　part；　because　he　had　provoked　small　and　partial　explosions；　or　rather　little　flames；　enough　t