Abstract: An edge detection method includes preparing a transparent substrate which includes a first main face having a first main region and a first peripheral region and a second main face having a second main region and a second peripheral region, the first peripheral region having an inclination angle of ?a1 and the second peripheral region having an inclination angle of ?a2, causing measuring light to enter the first peripheral region from a direction perpendicular to the first main region, detecting a non-emitting region where the measuring light is not emitted from the second peripheral region, and detecting an edge of the transparent substrate on the basis of the non-emitting region, wherein if a refractive index of the transparent substrate is n, the inclination angles ?a1 and ?a2satisfy the following expression: n×sin(?a1+?a2?arcsin(sin ?a1/n))?1.

Abstract: An edge detection method includes preparing a transparent substrate which includes a first main face having a first main region and a first peripheral region and a second main face having a second main region and a second peripheral region, the first peripheral region having an inclination angle of ?a1 and the second peripheral region having an inclination angle of ?a2, causing measuring light to enter the first peripheral region from a direction perpendicular to the first main region, detecting a non-emitting region where the measuring light is not emitted from the second peripheral region, and detecting an edge of the transparent substrate on the basis of the non-emitting region, wherein if a refractive index of the transparent substrate is n, the inclination angles ?a1 and ?a2 satisfy the following expression: n×sin(?a1+?a2?arcsin(sin ?a1/n))?1

Abstract: An object of the present invention is to provide an iron base Si--Mn alloy or an iron base Si--Mn--Ni alloy which can be easily crushed and can be manufactured in large quantity, and alloy powder thereof.An iron base Si--Mn--Ni alloy having good crushability and alloy powder thereof, comprising:C: 0.40 to 1.20% by weight,Si: 5.0 to 12.0% by weight,Mn: 19.0 to 42.0 % by weight, or Ni: not more than 30% by weight, and the balance being Fe, with the following equations satisfied: Si.gtoreq.11.89-2.92 C-0.077 Mn, Vickers hardness (Hv).gtoreq.550, and area ratio of dendrite structure .ltoreq.50%.An iron base Si--Mn--Ni alloy having good crushability and alloy powder thereof, comprising:C: 0.40 to 1.20% by weight,Si: 5.0 to 12.0% by weight,Mn: 19.0 to 42.0% by weight, or Ni: not more than 30% by weight, and the balance being Fe, with the following equations satisfied: Si.ltoreq.8.3 C+0.14 Mn, and relative permeability (.mu.).ltoreq.1.10.