The coupling capacitance of the wiring portions of a thermal type flow rate measuring apparatus is reduced so as to prevent a drop in the response characteristics. The emulsions are of the type oil-in-water. In the electrowinning method, a metal can be recovered from an aqueous solution containing a low concentration of metal ions using the above cyclone-shaped electrowinning apparatus. Therefore, a compact, relatively inexpensive, and above all, quick acting process is needed. Also disclosed is a high-pressure discharge lamp having a tubular outer piston, wherein the outer piston of the high-pressure discharge lamp has an aforesaid high-voltage pulse generator.