The owners of certain furniture delivered it on hire to one of two joint tenants of certain premises under an agreement whereby it was agreed that during the continuance of the hiring the hirer should pay to the owners by way of rent for the use and hire of the furniture 10s. per week. The agreement contained the following provisions: "If the hirer shall duly observe and perform the provisions and stipulations of this agreement ... and shall ... pay to the owners rents amounting in the aggregate ... to the sum of 73l. 12s. ... the hiring shall determine and the owners will at the option of the hirer assign all their interest in the said chattels to the hirer but until all the said payments shall have been made and the said covenants and agreements performed and such option shall be exercised the said chattels shall remain the sole