Cosmic Microwave Background Anisotropy at Degree Angular Scales and the Thermal History of the Universe

We study the anisotropy of the cosmic microwave background (CMB) in cold mixed dark matter (CDM and MDM) models, with non--scale-invariant power spectra (i. e. , n\1) and a late, sudden reionization the intergalactic medium at redshift zrh. We test these models recent detections of CMB anisotropy at large and intermediate scales. We find that current CMB anisotropy measurements cannot between CDM and MDM models. Our likelihood analysis that models with blue power spectra (n \\~{= 1. 2) and a at zrh \\~ 20 are most consistent with the anisotropy data here. Without reionization our analysis gives 1. 0 \= n \= 1. 26 (95\\% confidence limit) for Omega b = 0. 05. }