AR S

Near-infrared spectroscopy, at high altitude and low humidity to reduc e telluric absorption, has been carried out to accurately measure [Ar III]lambda7136 and [S III]lambda9069 in the metal-poor blue compact ir regular galaxies I Zw 18 and II Zw 40. Detailed modeling of the spectr a reveals that the ratio of the line intensities is insensitive to ion ization structure, being determined almost wholly by the electron temp erature and the ratio of the number abundances of argon and sulfur. I Zw 18, the SMC, the LMC, Galactic H II regions, Galactic planetary neb ulae, and the solar system, all have n(Ar)/n(S) within 10% of 0.21, wi th no evidence of any trend with metallicity (spanning a factor of 40 in the oxygen abundance). However, the result for II Zw 40 is inexplic ably higher by a factor of 2. Nevertheless, the line ratio I([Ar III]l ambda7136)/I([S III]lambda9069) shows considerable promise as a diagno stic of temperature, and thus abundances, in cool, metal-rich nebulae.